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Mathematics

A(-3, b) and B(1, b + 4) are two points. If the coordinates of the mid-point of AB are (-1, 1), then the value of b is :

  1. -1

  2. 0

  3. 1

  4. 2

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Answer

Given,

Mid-point of AB = (-1, 1).

A(-3, b) and B(1, b + 4) are two points. If the coordinates of the mid-point of AB are (-1, 1), then the value of b is : Reflection, RSA Mathematics Solutions ICSE Class 10.

By mid-point formula,

(x, y) = (x1+x22,y1+y22)\Big(\dfrac{x1 + x2}{2}, \dfrac{y1 + y2}{2}\Big)

Substituting values we get :

(1,1)=(3+12,b+(b+4)2)(1,1)=(22,2b+42)(1,1)=(1,b+2)\Rightarrow (-1, 1) = \Big(\dfrac{-3 + 1}{2}, \dfrac{b + (b + 4)}{2}\Big) \\[1em] \Rightarrow (-1, 1) = \Big(\dfrac{-2}{2}, \dfrac{2b + 4}{2}\Big) \\[1em] \Rightarrow (-1, 1) = (-1, b + 2)

Comparing the y-coordinates, we get :

⇒ 1 = b + 2

⇒ b = -1.

Hence, Option 1 is the correct option.

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