Distance Between Two Points With Examples<\/strong><\/h2>\nExample 1:<\/strong> \u00a0 \u00a0Find the distance between two points
\n(i) P(\u20136, 7) and Q(\u20131, \u20135)
\n(ii) R(a + b, a \u2013 b) and S(a \u2013 b, \u2013a \u2013 b)
\n\\(\\left( \\text{iii} \\right)\\text{ A(at}_{1}^{2}\\text{, 2a}{{\\text{t}}_{1}}\\text{) and B(at}_{2}^{2}\\text{, 2a}{{\\text{t}}_{2}}\\text{)}\\)
\nSol.<\/strong> \u00a0 \u00a0(i)<\/strong> Here, \u00a0x1<\/sub>\u00a0= \u2013 6, y1<\/sub> = 7 and x2<\/sub> = \u2013 1, y2<\/sub> = \u2013 5
\n\u2234 \u00a0\\( PQ=\\sqrt{{{\\left( {{x}_{2}}-{{x}_{1}} \\right)}^{2}}+{{\\left( {{y}_{2}}-{{y}_{1}} \\right)}^{2}}} \\)
\n\\( \\Rightarrow PQ=\\sqrt{{{(-1+6)}^{2}}+{{(-5-7)}^{2}}} \\\\ \\)
\n\\( \\Rightarrow PQ=\\sqrt{25+144}=\\sqrt{169}=13 \\)
\n(ii)<\/strong> We have,
\n\\( RS=\\sqrt{{{(a-b-a-b)}^{2}}+{{(-a-b-a+b)}^{2}}} \\)
\n\\( \\Rightarrow RS=\\sqrt{4{{b}^{2}}+4{{a}^{2}}}=2\\sqrt{{{a}^{2}}+{{b}^{2}}} \\)
\n(iii)<\/strong> We have,
\n\\( AB=\\sqrt{{{(a{{t}_{2}}^{2}-a{{t}_{1}}^{2})}^{2}}+{{(2a{{t}_{2}}-2a{{t}_{1}})}^{2}}} \\)
\n\\( \\Rightarrow AB=\\sqrt{{{a}^{2}}{{({{t}_{2}}-{{t}_{1}})}^{2}}{{({{t}_{2}}+{{t}_{1}})}^{2}}+4{{a}^{2}}{{({{t}_{2}}-{{t}_{1}})}^{2}}} \\)
\n\\(\\Rightarrow AB=a({{t}_{2}}-{{t}_{1}})\\sqrt{{{({{t}_{2}}+{{t}_{1}})}^{2}}+4}\\)<\/p>\nExample 2:<\/strong> \u00a0 \u00a0If the point (x, y) is equidistant from the points (a + b, b \u2013 a) and (a \u2013 b, a + b), prove that bx = ay.
\nSol.<\/strong> \u00a0 \u00a0Let P(x, y), Q(a + b, b \u2013 a) and R (a \u2013 b, a + b) be the given points. Then
\nPQ = PR\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0(Given)
\n\\(\\Rightarrow \\sqrt{{{\\{x-(a+b)\\}}^{2}}+{{\\{y-(b-a)\\}}^{2}}}=\\sqrt{{{\\{x-(a-b)\\}}^{2}}+{{\\{y-(a+b)\\}}^{2}}}\\)
\n\u21d2 {x \u2013 (a + b)}2<\/sup> + {y \u2013 (b \u2013 a)}2<\/sup> = {x \u2013 (a \u2013 b)}2<\/sup> + {y \u2013 (a + b)}2<\/sup>
\n\u21d2 x2<\/sup>\u00a0\u2013 2x (a + b) + (a + b)2<\/sup> + y2<\/sup> \u2013 2y (b \u2013 a) + (b \u2013 a)2<\/sup> = x2<\/sup>\u00a0+ (a \u2013 b)2<\/sup> \u2013 2x(a \u2013 b) + y2<\/sup> \u2013 2 (a + b) + (a + b)2<\/sup>
\n\u21d2 \u20132x (a + b) \u2013 2y (b \u2013 a) = \u2013 2x (a \u2013 b) \u2013 2y (a + b)
\n\u21d2 ax + bx + by \u2013 ay = ax \u2013 bx + ay + by
\n\u21d2 2bx = 2ay \u21d2\u00a0bx = ay<\/p>\nExample 3:<\/strong> \u00a0 \u00a0Find the value of x, if the distance between the points (x, \u2013 1) and (3, 2) is 5.
\nSol. \u00a0\u00a0<\/strong> Let P(x, \u2013 1) and Q(3, 2) be the given points, Then,
\nPQ = 5 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 (Given)
\n\\(\\Rightarrow \\sqrt{{{(x-3)}^{2}}+{{(-1-2)}^{2}}}=5\\)
\n\u21d2 (x \u2013 3)2<\/sup> + 9 = 52<\/sup>
\n\u21d2 x2<\/sup>\u00a0\u2013 6x + 18 = 25 \u00a0\u00a0\u21d2 \u00a0x2<\/sup>\u00a0\u2013 6x \u2013 7 = 0
\n\u21d2 (x \u2013 7) (x + 1) = 0 \u00a0\u00a0\u21d2 \u00a0x = 7 or x = \u2013 1<\/p>\nExample 4:<\/strong>\u00a0 \u00a0 \u00a0Show that the points (a, a), (\u2013a, \u2013a) and (\u2013\u00a0\u221a3 a, \u221a3 a) are the vertices of an equilateral triangle. Also find its area.
\nSol. \u00a0\u00a0<\/strong> Let A (a, a), B(\u2013a, \u2013a) and C(\u2013\u00a0\u221a3 a, \u221a3 a) be the given points. Then, we have
\n\\( AB=\\sqrt{{{(-a-a)}^{2}}+{{(-a-a)}^{2}}}=\\sqrt{4{{a}^{2}}+4{{a}^{2}}}=2\\sqrt{2}a \\)
\n\\( BC=\\sqrt{{{(-\\sqrt{3}a+a)}^{2}}+{{(\\sqrt{3}a+a)}^{2}}} \\)
\n\\( \\Rightarrow BC=\\sqrt{{{a}^{2}}{{(1-\\sqrt{3})}^{2}}+{{a}^{2}}{{(\\sqrt{3}+1)}^{2}}} \\)
\n\\( \\Rightarrow BC=a\\sqrt{1+3-2\\sqrt{3}+1+3+2\\sqrt{3}}=a\\sqrt{8}=2\\sqrt{2}a \\)
\n\\( and,\\text{ }AC=\\sqrt{(-\\sqrt{3}a-{{a}^{2}})+{{(\\sqrt{3}a-a)}^{2}}} \\\\ \\)
\n\\( \\Rightarrow AC=\\sqrt{{{a}^{2}}(\\sqrt{3}+1)+{{a}^{2}}{{(\\sqrt{3}-1)}^{2}}} \\)
\n\\( \\Rightarrow AC=\\sqrt{3+1+2\\sqrt{3}+3+1-2\\sqrt{3}}=a\\sqrt{8}=2\\sqrt{2}a \\)
\nClearly, we have
\nAB = BC = AC
\nHence, the triangle ABC formed by the given points is an equilateral triangle.
\nNow,
\nArea of \u2206ABC = \\(\\frac { \\sqrt { 3 } \u00a0}{ 4 } \\) \u00a0(side)2<\/sup>
\n\u21d2 Area of \u2206ABC = \\(\\frac { \\sqrt { 3 } \u00a0}{ 4 } \\) \u00d7 AB2<\/sup>
\n\u21d2 Area of \u2206ABC = \\(\\frac { \\sqrt { 3 } \u00a0}{ 4 } \\) \u00d7 (2\u221a2 a)2<\/sup> sq. units = 2\u221a3 a2<\/sup> sq. units<\/p>\nExample 5:<\/strong>\u00a0 \u00a0 \u00a0Show that the points (1, \u2013 1), (5, 2) and (9, 5) are collinear.
\nSol.<\/strong>\u00a0 \u00a0 Let A (1, \u20131), B (5, 2) and C (9, 5) be the given points. Then, we have\u00a0Clearly, AC = AB + BC
\n\\( AB=\\sqrt{{{(5-1)}^{2}}+{{(2+1)}^{2}}}=\\sqrt{16+9}=5 \\)
\n\\( BC=\\sqrt{{{(5-9)}^{2}}+{{(2-5)}^{2}}}=\\sqrt{16+9}=5 \\)
\n\\( and,~~~~~AC=\\sqrt{{{(1-9)}^{2}}+{{(-1-5)}^{2}}}=\\sqrt{64+36}=10 \\)
\nHence, A, B, C are collinear points.<\/p>\nExample 6:<\/strong>\u00a0 \u00a0 \u00a0Show that four points (0, \u2013 1), (6, 7), (\u20132, 3) and (8, 3) are the vertices of a rectangle. Also, find its area.
\nSol. \u00a0\u00a0<\/strong> Let A (0, \u20131), B(6, 7), C(\u20132, 3) and D (8, 3) be the given points. Then,
\n\\( AD=\\sqrt{{{(8-0)}^{2}}+{{(3+1)}^{2}}}=\\sqrt{64+16}=4\\sqrt{5} \\)
\n\\( BC=\\sqrt{{{(6+2)}^{2}}+{{(7-3)}^{2}}}=\\sqrt{64+16}=4\\sqrt{5} \\)
\n\\( AC=\\sqrt{{{(-2-0)}^{2}}+{{(3+1)}^{2}}}=\\sqrt{4+16}=2\\sqrt{5} \\)
\n\\( and,\\text{ }BD\\text{ }=\\sqrt{{{(8-6)}^{2}}+{{(3-7)}^{2}}}=\\sqrt{4+16}=2\\sqrt{5} \\)
\n\u2234 AD = BC and AC = BD.
\nSo, ADBC is a parallelogram,
\n
\n\\( Now,\\text{ }AB\\text{ }=\\sqrt{{{(6-0)}^{2}}+{{(7+1)}^{2}}}=\\sqrt{36+64}=10 \\)
\n\\( and~~~~~~CD\\text{ }=\\sqrt{{{(8+2)}^{2}}+{{(3-3)}^{2}}}=10 \\)
\nClearly, AB2<\/sup> = AD2<\/sup> + DB2<\/sup> and CD2<\/sup> = CB2<\/sup> + BD2<\/sup>
\nHence, ADBC is a rectangle.
\nNow, Area of rectangle ADBC = AD \u00d7 DB
\n= (4\u221a5 \u00d7 2\u221a5 ) sq. units = 40 sq. units<\/p>\nExample 7:<\/strong>\u00a0 \u00a0 \u00a0If P and Q are two points whose coordinates are (at2<\/sup>, 2at) and (a\/t2<\/sup>, 2a\/t) respectively and S is the point (a, 0). Show that \u00a0 \u00a0\\(\\frac{1}{SP}+\\frac{1}{SQ}\\) \u00a0is independent of t.
\nSol. \u00a0\u00a0<\/strong> We have,
\n\\( SP=\\sqrt{{{(a{{t}^{2}}-a)}^{2}}+{{(2at-0)}^{2}}} \\)
\n\\( =\\sqrt{{{({{t}^{2}}-1)}^{2}}+4{{t}^{2}}}=a({{t}^{2}}+\\text{ }1) \\)
\n\\( and~~~~~~SQ\\text{ }=\\sqrt{{{\\left( \\frac{a}{{{t}^{2}}}-a \\right)}^{2}}+{{\\left( \\frac{2a}{t}-0 \\right)}^{2}}} \\)
\n\\( \\Rightarrow SQ\\text{ }=\\sqrt{\\frac{{{a}^{2}}{{(1-{{t}^{2}})}^{2}}}{{{t}^{4}}}+\\frac{4{{a}^{2}}}{{{t}^{2}}}} \\)
\n\\( \\Rightarrow SQ\\text{ }=\\frac{a}{{{t}^{2}}}\\sqrt{{{(1-{{t}^{2}})}^{2}}+4{{t}^{2}}}=\\frac{a}{{{t}^{2}}}\\sqrt{{{(1+{{t}^{2}})}^{2}}} \\)
\nwhich is independent of t.
\n\\( =~\\frac{a}{{{t}^{2}}}(1\\text{ }+\\text{ }{{t}^{2}})~ \\)
\n
\n\\( \\Rightarrow \\frac{1}{SP}+\\frac{1}{SQ}=\\frac{1+{{t}^{2}}}{a({{t}^{2}}+1)}=\\frac{1}{a} \\)<\/p>\nExample 8:<\/strong>\u00a0 \u00a0 \u00a0If two vertices of an equilateral triangle be (0, 0), (3, \u221a3 ), find the third vertex.
\nSol. \u00a0\u00a0<\/strong> O(0, 0) and A(3, \u221a3) be the given points and let B(x, y) be the third vertex of equilateral \u2206OAB. Then, OA = OB = AB
\n\u21d2 \u00a0OA2<\/sup> = OB2<\/sup> = AB2<\/sup>
\n
\nWe have, OA2\u00a0<\/sup>= (3 \u2013 0)2<\/sup> + (\u221a3 \u2013 0)2<\/sup> = 12,
\nOB2\u00a0<\/sup>= x2<\/sup>\u00a0+ y2<\/sup>
\nand, AB2\u00a0<\/sup>= (x \u2013 3)2<\/sup>+ (y \u2013 \u221a3)2<\/sup>
\n\u21d2 \u00a0AB2<\/sup> = x2<\/sup> + y2<\/sup> \u2013 6x \u2013 2 y + 12
\n\u2234 OA2<\/sup> = OB2<\/sup> = AB2<\/sup>
\n\u21d2 \u00a0OA2<\/sup> = OB2<\/sup> and OB2<\/sup> = AB2<\/sup>
\n\u21d2 \u00a0x2<\/sup>\u00a0+ y2<\/sup> = 12
\nand, x2<\/sup>\u00a0+ y2<\/sup> = x2<\/sup>\u00a0+ y2<\/sup> \u2013 6x \u2013 2 \u221a3y + 12
\n\u21d2 \u00a0x2<\/sup>\u00a0+ y2<\/sup> = 12 and 6x + 2 \u221a3y = 12
\n\u21d2 \u00a0x2<\/sup>\u00a0+ y2<\/sup> = 12 and 3x + \u221a3y = 6
\n\\( \\Rightarrow \\text{ }~{{x}^{2}}~+\\text{ }{{\\left( \\frac{6-3x}{\\sqrt{3}} \\right)}^{2}}=\\text{ }12\\text{ }\\left[ \\because \\ 3x+\\sqrt{3}y=6\\ \\ \\therefore \\ \\ y=\\frac{6-3x}{\\sqrt{3}} \\right] \\)
\n\u21d2 \u00a03x2<\/sup> + (6 \u2013 3x)2<\/sup> = 36
\n\u21d2 \u00a012x2<\/sup> \u2013 36x = 0 \u00a0 \u00a0 \u21d2 \u00a0 \u00a0 x = 0, 3
\n\u2234 \u00a0x = 0 \u00a0\u21d2 \u00a0\u00a0\u221a3y = 6
\n\\( \\Rightarrow \\text{ }y=\\frac{6}{\\sqrt{3}}=2\\sqrt{3}\\text{ }\\left[ \\text{Putting}\\ \\text{x}=\\text{0}\\ \\text{in 3x + }\\sqrt{\\text{3}}\\text{y}=\\text{6} \\right] \\)
\nand, x = 3 \u21d2 \u00a0\u00a09 +\u00a0\u221a3 y = 6
\n\\(\\Rightarrow \\text{ }y=\\frac{6-9}{\\sqrt{3}}=-\\sqrt{3}\\text{ \u00a0 \u00a0}\\left[ \\text{Putting}\\ \\text{x}=\\text{0}\\ \\text{in 3x + }\\sqrt{\\text{3}}\\text{y}=\\text{6} \\right]\\)
\nHence, the coordinates of the third vertex B are (0, 2 \u221a3) or (3, \u2013 \u221a3).<\/p>\nExample 9:<\/strong>\u00a0 \u00a0 \u00a0Find the coordinates of the circumcentre of the triangle whose vertices are (8, 6), (8, \u2013 2) and (2, \u2013 2). Also, find its circum radius.
\nSol. \u00a0\u00a0<\/strong> Recall that the circumcentre of a triangle is equidistant from the vertices of a triangle. Let A (8, 6), B(8, \u20132) and C(2, \u2013 2) be the vertices of the given triangle and let P (x, y) be the circumcentre of this triangle. Then,
\nPA = PB = PC \u21d2 \u00a0\u00a0PA2<\/sup> = PB2<\/sup> = PC2<\/sup>
\n
\nNow, PA2<\/sup> = PB2<\/sup>
\n\u21d2 \u00a0(x \u2013 8)2<\/sup> + (y \u2013 6)2<\/sup> = (x \u2013 8)2 + (y + 2)2<\/sup>
\n\u21d2 \u00a0x2<\/sup> + y2<\/sup> \u2013 16x \u2013 12y + 100 = x2<\/sup> + y2<\/sup> \u2013 16x + 4y + 68
\n\u21d2 \u00a016y = 32 \u21d2 \u00a0\u00a0y = 2
\nand, PB2<\/sup> = PC2<\/sup>
\n\u21d2 \u00a0(x \u2013 8)2<\/sup> + (y + 2)2<\/sup> = (x \u2013 2)2<\/sup> + (y + 2)2<\/sup>
\n\u21d2 \u00a0x2<\/sup> + y2<\/sup> \u2013 16x + 4y + 68 = x2<\/sup>\u00a0+ y2<\/sup> \u2013 4x + 4y + 8
\n\u21d2 \u00a012x = 60 \u21d2 \u00a0\u00a0x = 5
\nSo, the coordinates of the circumcentre P are (5, 2).
\nAlso, Circum-radius = PA = PB = PC
\n\\(=\\sqrt{{{(5-8)}^{2}}+{{(2-6)}^{2}}}=\\sqrt{9+16}=5\\)<\/p>\nExample 10:<\/strong>\u00a0 \u00a0 \u00a0If the opposite vertices of a square are (1, \u2013 1) and (3, 4), find the coordinates of the remaining angular points.
\nSol.<\/strong>\u00a0 \u00a0 Let A(1, \u2013 1) and C(3, 4) be the two opposite vertices of a square ABCD and let B(x, y) be the third vertex.
\n
\nThen, AB = BC
\n\u21d2 \u00a0AB2<\/sup> = BC2<\/sup>
\n\u21d2 \u00a0(x \u2013 1)2<\/sup> + (y + 1)2<\/sup> = (3 \u2013 x)2<\/sup> + (4 \u2013 y)2<\/sup>
\n\u21d2 \u00a0x2<\/sup>\u00a0\u2013 2x + 1 + y2<\/sup> + 2y + 1 = 9 \u2013 6x + x2<\/sup>\u00a0+ 16 \u2013 8y + y2
\n\u21d2 \u00a0x2<\/sup> + y2<\/sup> \u2013 2x + 2y + 2 = x2<\/sup> + y2<\/sup> \u2013 6x \u2013 8y + 25
\n\u21d2 \u00a04x + 10y = 23
\n\u21d2 \u00a0x = \u00a0 \\(\\frac { 23-10y }{ 4 }\\)\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u2026.(1)
\nIn right-angled triangle ABC, we have
\nAB2<\/sup> + BC2<\/sup> = AC2<\/sup>
\n\u21d2 \u00a0(x \u2013 3)2<\/sup> + (y \u2013 4)2<\/sup> + (x \u2013 1)2<\/sup> + (y + 1)2<\/sup> = (3 \u20131)2<\/sup> + (4 + 1)2<\/sup>
\n\u21d2 \u00a0x2<\/sup>\u00a0+ y2<\/sup> \u2013 4x \u2013 3y \u2013 1 = 0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 …. (2)
\nSubstituting the value of x from (1) and (2),
\nwe get
\n\\({{\\left( \\frac{23-10y}{4} \\right)}^{2}}\\)+ y2<\/sup> \u2013 (23 \u2013 10y) \u2013 3y \u2013 1 = 0
\n\u21d2 \u00a04y2<\/sup> \u2013 12y + 5 = 0 \u00a0\u00a0\u21d2 \u00a0\u00a0(2y \u2013 1) (2y \u2013 5) = 0
\n\u21d2 \u00a0y = \u00a0\\(\\frac { 1 }{ 2 }\\) \u00a0 or \u00a0\\(\\frac { 5 }{ 2 }\\)
\nPutting y = \\(\\frac { 1 }{ 2 }\\) \u00a0 and y = \\(\\frac { 5 }{ 2 }\\)respectively in (1) we get
\nx = \\(\\frac { 9 }{ 2 }\\) \u00a0 and x = \\(\\frac { -1 }{ 2 }\\) \u00a0 \u00a0respectively.
\nHence, the required vertices of the square are \u00a0\\(\\left( \\frac{9}{2},\\ \\frac{1}{2} \\right)\\text{ \u00a0and \u00a0}\\left( -\\frac{1}{2},\\ \\frac{5}{2} \\right) \\).<\/p>\nExample 11:<\/strong>\u00a0 \u00a0 \u00a0Prove that the points (\u20133, 0), (1, \u20133) and (4, 1) are the vertices of an isosceles right angled triangle. Find the area of this triangle.
\nSol. \u00a0\u00a0<\/strong> Let A (\u20133, 0), B (1, \u20133) and C (4, 1) be the given points. Then,