①√2(√3+√5)②(√80+√40)÷√5③(√5+3)(5+2)
④(√a+√b)(3√a-√b)
计算;
①(4+√7)(4-√7)②(√6+√2)(√6-√2)③(√3+2)²
④(2√5-√2)²