## Precalculus: Mathematics for Calculus, 7th Edition

(A + B)(A - B) 25 - $x^2$
The Special Product Formula for the product of a sum and a difference of terms is: (A + B)(A - B) = $A^2$ - $B^2$ The Special Factor Formula is simply the reverse of this, where: $A^2$ - $B^2$ = (A + B)(A - B) Therefore if A = 4$x^2$ and B = 25, then 4$x^2$ - 25 = (2x + 5)(2x - 5), as 2x is the square root of $4x^2$ and 5 is the square root of 25