## Algebra 1

We use the formula for the difference of squares to apply to this question. The difference of squares formula is: $(a-b) (a+b) = a^{2} - b^{2}$ = $9n^{2}$ - 400 *** Take the square root of $9n^{2}$ which is 3n. Becuase 3n × 3n= $9n^{2}$ *** Take the square root of 400 which is 20. Becuase 20 × 20= 400 = $(3n)^{2}−20^{2}$ In the given formula let 3n represents a and 20 represents b. $(3n)^{2}−20^{2}$ = (3n+20)(3n-20)