Determine which polynomial is a perfect square trinomial.

25x^2 − 40x − 16

9a^2 − 20a − 25

25b^2 − 15b + 9

16x^2 − 56x + 49

Question

Determine which polynomial is a perfect square trinomial. 

 25x^2 − 40x − 16 

 9a^2 − 20a − 25 

 25b^2 − 15b + 9 

 16x^2 − 56x + 49

cwrw238 · Answer

note it cant be the first or second choice because there are no real square roots of -16 or -25

anonymous · Answer

well ow is it one of the last two? i cant find one that works

cwrw238 · Answer

oh  sorry - my mistake -  you have to multiply them then add

take the the third one:
 
 25b^2 − 15b + 9 

you have sqrt25 = 5 and sqrt 9 = -3  ( i took negative sqrt becuse of the -15x)

so that 5 * -3 = - 15   and -15 + -15 = -30    - so cant be this one

anonymous · Answer

okay, so it would be the last one?

cwrw238 · Answer

4th option 

we got

16x^2 − 56x + 49 

sqrt 16 = 4 and sqrt 49 = -7
so
4 * -7 = -28   and  -28 + -28 = -56

we got the one

anonymous · Answer

okay thank you

cwrw238 · Answer

you can check it out by the distributive law;

(4x - 7)(4x -7 ) = 16x^2 -28x - 28x + 49 = 16x^2 - 56x + 49

cwrw238 · Answer

yw