Distributive Property: a ( b + c) = (a*b) + (a*c)
b)  x(x + 9) = x*x + 9*x 
 = x² + 9x 
c) x² - 18x 
 x² = x * x
 18x = 18 *x
 G C F = x
Greatest common factor in both the terms is 'x'.Take the common variable from both the terms.
x² - 18x = x*x - 18*x
 = x (x - 18)
 
Standard form. Factored form
 x² x*x
 x² + 9x x(x +9)
 x² - 18x x(x - 18) 
-x² + 10x x(-x + 10) = x(10 -x)
-x² - 2.75x -x(x + 2.75)