(x - 15)*(15 + x)
(x - 1*15)*(15 + x)
1*(x + 15)*(x - 15)
(1*(x + 15))*(x - 15)
2 -225 + x
-225 + x^2
(15.0 + x)*(-15.0 + x)
(-15 + x)*(15 + x)