x1,x2是方程x²-3x-5=0
x1²+x2²
=(x1+x2)²-2x1x2
=3²-2*(-5)
=9+10
=19
(x1+x2)²
=3²
=9
另一个题
x1²x2²-x1-x2=115
k²-6=115
k²=121
k=±11
又判别式=36-4k≥0
k≤9
因此,k=11舍,
k=-11
x1²+x2²+8
=(x1+x2)²-2x1x2+8
=6²+22+8
=66