Correct answer.
( a + b ) ^ 2 = a ^ 2 + 2 a b + b ^ 2
In this case :
a = 1
2 a b = 9
2 * 1 * b = 9
2 b = 9 Divide both sides by 2
b = 9 / 2
c = b ^ 2 = ( 9 / 2 ) ^ 2 = 81 / 4
( x + 9 / 2 ) ^ 2 = x ^ 2 + 9 x + ( 81 / 4 )
What is the value of c so that y=x^2+9x+c is a perfect square trinomial?
A. 18
B. 9/2
C. 9/4
D. 81/4
My answer is D.
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