Posted by **Shadow** on Sunday, March 25, 2012 at 9:52pm.

What positive value of b makes 9^2-bx+4 a perfect square trinomial? How would you solve this problem? Thanks

- Math -
**Shadow**, Sunday, March 25, 2012 at 9:52pm
9x^2-bx+4

- Math -
**Reiny**, Sunday, March 25, 2012 at 10:07pm
First of all to be a perfect square, the first and last terms should be perfect squares, and they are!

so it looks like we had

(3x ± 2)^2

for (3x+2)^2 we would get 9x^2 + 12x + 4

so -bx = 12x

b = -12

for (3x - 2)^2 we would get 9x^2 - 12x + 4

so -bx = -12x

b = 12

So b = ± 12

- Math -
**Shadow**, Sunday, March 25, 2012 at 10:11pm
Thank you!

- Math -
**Reiny**, Sunday, March 25, 2012 at 10:17pm
Welcome

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