SOLUTION: What value of c makes the polynomial below a perfect square? 4x^2+12x+c

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: What value of c makes the polynomial below a perfect square? 4x^2+12x+c      Log On


   

Question 621893: What value of c makes the polynomial below a perfect square?
4x^2+12x+c
Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
+4x%5E2 is the square of 2x
%282x%2Bb%29%5E2=4x%5E2%2B4bx%2Bb%5E2
If 4bx=12x
no matter what value x takes, it must be
4b=12 <---> b=3 and then
%282x%2Bb%29%5E2=%282x%2B3%29%5E2=4x%5E2%2B12x%2B3%5E2=4x%5E2%2B12x%2B9
So highlight%28c=9%29