# Math

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

• Math -

9x^2-bx+4

• Math -

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 -

Thank you!

• Math -

Welcome

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