(2√5+1)(2√5-1)=(2√5)²-1²=20-1=19
(a+√c)(a-√c)=a²-(√c)²=a²-c
(√x-√z)(√x+√z)=(√x)²-(√z)²=x-z
n²-7=n²-(√7)²=(n-√7)(n+√7)
81-y=9²-(√y)²=(9-√y)(9+√y)
√x+x=√x(1+√x)
√18+√22=3√2+√22=√2(3+√11)
3√a-3√b=3(√a-√b)
b-√b=√b(√b-1)
a√3-b√3=√3(a-b)
m√n+n√m=√(mn)*(√m+√n)
(2√5+1)(2√5-1)=(2√5)²-1²=20-1=19
(a+√c)(a-√c)=a²-(√c)²=a²-c
(√x-√z)(√x+√z)=(√x)²-(√z)²=x-z
n²-7=n²-(√7)²=(n-√7)(n+√7)
81-y=9²-(√y)²=(9-√y)(9+√y)
√x+x=√x(1+√x)
√18+√22=3√2+√22=√2(3+√11)
3√a-3√b=3(√a-√b)
b-√b=√b(√b-1)
a√3-b√3=√3(a-b)
m√n+n√m=√(mn)*(√m+√n)