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Answer:
100 will have to be added to both sides to complete the square
Step-by-step explanation:
Given:
x^2+20x+28=0
x² + 20x + 28 = 0
x² + 20x = -28
Using completing the square method of solving quadratic equation
Find the square of half of the coefficient of x
Coefficient of x = 20
Half of the coefficient of x = 20/2
= 10
Square of the half of the coefficient of x = 10²
= 100
Add the square of the half of the coefficient of x to both sides of the equation
x² + 20x = -28
x² + 20x + 100 = -28 + 100
(x + 10)² = 72
[tex]x^2 +20x -6 =0\\\\\implies x^2 + 2 \cdot 10 \cdot x +10^2 -10^2 -6 =0\\\\\implies (x +10)^2 -106=0\\\\\implies (x +10)^2 =106\\\\\implies x +10 = \pm\sqrt{106}\\\\\implies x = -10 \pm \sqrt{106}[/tex]