This type of statement is called a difference of squares. If you see an equation in the form:
a2 - b2
then it is also equal to:
(a + b)(a - b)
In this case 9x2, and 25 are both perfect squares. 9x2 is equal to (3x)2 and 25 is equal to 52, so the that statement can be factored out as:
(3x - 5)(3x + 5)
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(x + 2)(3x - 1)(3x + 1)
x2 - 9x + 20 = (x - 4)( x - 5)
You don't need to factor that; you can add them together, since they have the same variable.However, assuming you might mean 81x squared + 9x, you can take out the common factor, which is 9x.
x2 + 9x2 = 10x2
32 minus the product of 9 and a number is 140 the answer is 12. 32-9x=140 9x=108 x=12