1、（x-5）²-17（x-5）+30=0
(x-5-15)(x-5-2)=0
(x-20)(x-7)=0
x1=20 x2=7
x²-2（√3+√5）x+4√15=0
(x-2√3)(x-2√5)=0
x1=2√3,x2=2√5