x²-（k+1）x+k+2=0判别式△=(k+1)²-4(k+2)=k²+2k+1-4k-8=k²-2k-7≥0 ①两根之和为 x1+x2=k+1两根之积为 x1x2=k+2则 两根的平方和为 (x1+x2)²-2x1x2=(k+1)²-2(k+2)=k²+2k+1-2k-4=...