Question

Which polynomial is a perfect square trinomial?

36x2 − 18x − 9
4a2 − 28a − 49
25b2 − 40b + 16
4x2 − 6x + 9

Answer 1

25b^2 -40b +16 = (5b -4)^2 

so this is the right answer sure 

Answer 2

Answer:

Option 3rd is correct

$25b^2-40b+16$

Step-by-step explanation:

Formula for perfect square trinomial is given by:

$(a-b)^2 = a^2-2ab+b^2$

From the given options:

A polynomial which is a perfect square trinomial is, $25b^2-40b+16$

Since,

We can write this as:

$25b^2-40b+16 = (5b)^2-2 \cdot (5b) \cdot 4+4^2$

Apply the formula we have;

$25b^2-40b+16 = (5b-4)^2$

Therefore, $25b^2-40b+16$ is a perfect square trinomial