simplify by collecting like terms if possible
7sqrt20-8sqrt5
7 * sqrt 20 = 7 * sqrt 5 * sqrt 4
= 7* sqrt5 * 2 = 14sqrt5
so (14sqrt5) - (8sqrt5)= 6sqrt5
7sqrt20-8sqrt5
= 7* sqrt5 * 2 = 14sqrt5
so (14sqrt5) - (8sqrt5)= 6sqrt5