设x1 x2是一元二次方程2x²-3x-5=0的两个根求x1²+3x2²-3x2

2x²-3x-5=0
2x2²-3x2-5=0
2x2²-3x2=5
x1+x2=3/2
x1*x2=-5/2
x1²+3x2²-3x2
=x1²+x2²+2x2²-3x2
=x1²+x2²+5
=x1²+2x1x2+x2²-2x1x2+5
=(x1+x2)²-2x1x2+5
=(3/2)²-2*(-5/2)+5
=9/4+5+5
=49/4