Answer: Choice A
It factors to (x - 0.9)(x + 0.9)
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Work Shown:
[tex]x^2 - 0.81\\\\x^2 - (0.9)^2\\\\(x-0.9)(x+0.9)[/tex]
I used the difference of squares factoring rule. The order of the factors doesn't matter. So an alternative answer is (x+0.9)(x-0.9)
