Question

Which polynomial is a perfect square trinomial?

A. 36x²-18x-9
B. 4a²-28a-49
C. 25b²-40b+16
D. 4x²-6x+9

Answer 1

C
//Brief explanation
Using a discriminant (b^2 - 4ac), for a perfect square the discriminant = 0.
For A the discriminant is >0 (1620)
For B the discriminant is >0 (1568)
For C the discriminant = 0
For D the discriminant is < 0 (-108)

Answer 2

ANSWER: C
because of how the multiples of 25 are 5 and 5 and the multiples of 16 can be -4,-4...
5*-4+5*-4=-40
(5x-4)²= ((5²)x²-40x+(-4²))=25x²-40+16