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Mathematics

If the distance between the points (2, -2) and (-1, x) is 5 units, then one of the value of x is

  1. -2

  2. 2

  3. -1

  4. 1

Coordinate Geometry

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Answer

By distance formula,

d = (x2x1)2+(y2y1)2\sqrt{(x2 - x1)^2 + (y2 - y1)^2}

Given,

Distance between (2, -2) and (-1, x) is 5 units.

5=(12)2+[x(2)]25=(3)2+[x+2]25=9+x2+4+4x5=x2+4x+13x2+4x+13=52 [On squaring both sides]x2+4x+13=25x2+4x12=0x2+6x2x12=0x(x+6)2(x+6)=0(x2)(x+6)=0x2=0 or x+6=0x=2 or x=6.\therefore 5 = \sqrt{(-1 - 2)^2 + [x - (-2)]^2} \\[1em] \Rightarrow 5 = \sqrt{(-3)^2 + [x + 2]^2} \\[1em] \Rightarrow 5 = \sqrt{9 + x^2 + 4 + 4x} \\[1em] \Rightarrow 5 = \sqrt{x^2 + 4x + 13} \\[1em] \Rightarrow x^2 + 4x + 13 = 5^2 \text{ [On squaring both sides]} \\[1em] \Rightarrow x^2 + 4x + 13 = 25 \\[1em] \Rightarrow x^2 + 4x - 12 = 0 \\[1em] \Rightarrow x^2 + 6x - 2x - 12 = 0 \\[1em] \Rightarrow x(x + 6) - 2(x + 6) = 0 \\[1em] \Rightarrow (x - 2)(x + 6) = 0 \\[1em] \Rightarrow x - 2 = 0 \text{ or } x + 6 = 0 \\[1em] \Rightarrow x = 2 \text{ or } x = -6.

As distance cannot be negative,

∴ x = 2

Hence, Option 2 is the correct option.

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