Find the value of c to complete the square: x^2+8x+c

So, c must be 121 to make the trinomial a perfect square. 3. x. 2. + 9x + c. SOLUTION: Page 1. 9-4 Solving Quadratic Equations by Completing the Square + 4x = 6. SOLUTION: The solutions are about –5.2 and 1.2. 6. x. 2. − 8x = −9.

X^2+8x+c 

You can only go so far with this equation. 
Step 1: Add -x^2 to both sides. 
x^2+c+8x+ (-x^2) =0+ (-x^2)
c+8x=-x^2
Step 2: Add -8x to both sides. 
c+8x+ (-8x) =-x2+ (-8x)
c=-x^2-8x
c= -x^2-8x. 

Its equal to d=7.07in