Question

Determine which polynomial is a perfect square trinomial.

49x2 − 28x + 16

9a2 − 30a + 25

25b2 − 45b − 81

16x2 − 24x − 9

Answer 1

b

Explanation:

b

Answer 2

9a2 − 30a + 25

Explanation:

Perfect square trinomials follow these forms:

`(a+b)^2=a^2+2ab+b^2`

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

Notice that 25b2 − 45b − 81 and 16x2 − 24x − 9 have too many minus signs. They do not follow the form.

Notice that 49x2 − 28x + 16 would have a=7 and b=4. But 2ab should be 2*4*7=56. This does not follow the form.

Only 9a2 − 30a + 25 follows the form.