Question

Which polynomial is a perfect square trinomial?


49x^2 - 28x + 16
4a^2 - 20a + 25
25b^2 - 20b - 16
16x^2 - 24x - 9

Answer 1

second equation

Answer 2

can you explain why?

Answer 3

49x2−28x+16

Take the middle term −28 and then divide by two times the first term 2×49, then square it:
(−282×49)2=(−27)2=414
This must be equatl to the last term. Since 16≠4/14, this one isn't a perfect square.
You have to multiply the first term back
http://www.mathsisfun.com/algebra/completing-square.html

Answer 4

They said
d=b2a
You want e=0 to have a perfect square which means :
c=b24a
By the way
b24a=a(b2a)2
49x2−28x+16
So
b24a=(−28)24(49)=4≠16
4a2−20a+25
We use
b24a=(−20)24(4)=40016=25=c
So it is a complete square.
Do you understand how I put b and a into the equation?

Answer 5

Yes!

Answer 6

ANOTHER WAY TO SOLVE
b2=4ac
Would work, or even
b=4ac−−−√
But not
ac√=b
...

Answer 7

THANK YOU!

Answer 8

yeah :)