Question

Diego is solving the equation x2 – 12x = 21

Which value must be added to both sides of the equation to make the left side a perfect -square trinomial?

A

36

B

32

с

144

D

4

Answer 1

`36`

Explanation:

Given

`x^2 - 12x = 21`

Required

Make a perfect square

First, get the coefficient (k) of x

`k = -12`

Divide by 2

`(k)/(2) = (-12)/(2)`

`(k)/(2) = -6`

Square this result:

`((k)/(2))^2 = (-6)^2`

`((k)/(2))^2 = 36`

Hence, 36 when added to the left-hand side makes it a perfect square trinomial