Question

Add _____ to each side x2 – 8x = 9 to complete the square.

Answer 1

The correct answer is 25

Explanation:

It is given a quadratic equation,

x² – 8x = 9

To find the number to be added

The given equation be x² – 8x = 9

here we have to add (b/2)² - the square of half the coefficient of x,

Here b = -8

(b/2)² = (-8/2)² = -4² = 16

Add both side with 16

x² – 8x + 16 = 9 + 16

(x - 4)² = 25

(x - 4)² = 5²

Answer 2

16

Explanation:

We use the completing square method to find make the expression a perfect square.

(b/2)²=ac where a and b are coefficients of x² and x respectively while c is a constant.

= (-8/2)²=16

We add 16 to both sides and the expression becomes a perfect square.