x2是方程的根所以2x2²-3x2-5=02x²=3x2+5韦达定理x1+x2=3/2,x1x2=-5/2所以x1²+x2²=(x1+x2)²-2x1x2=9/4+5=29/4原式=x1²+x2²+2x2²-3x2=29/4+(3x2+5)-3x2=29/4+5=49/4...