1.

If points (1, 2), (-1, x) and (2, 3) are collinear, then x will be :(A) 2(B) 0(C) -1(D) 1

Answer»

Answer is (B) 0

Let the points A(1, 2), B(1, x) and C(2, 3) are collinear then area of triangle made by these points will be zero.

⇒ 1/2[x1(y2 – y3) + x2(y3 – y1) + x3(y1 – y2)]

⇒ 1/2[(x – 3) + (-1)(3 – 2) + 2(2 – x)] = 0

⇒ x – 3 – 1 + 2(2 – x) = 0

⇒ x – 3 – 1 + 4 – 2x = 0

⇒ -x – 4 + 4 = 0

⇒ x = 0



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