x²-5x-6=0（x-6）（x+1）=0x1=6，x2=-1（x²-10）²+3x²=28设x²=t（t-10）²+3t=28t²-20t+100+3t=28t²-17t+72=0（t-8）（t-9）=0t1=8，x1=-2√2，x2=2√2t2=9，x3=3，x4=-3
