(x-5)(x+3)=x²-2x-15
即x²+(p+q)x+pq=x²-2x-15
所以p+q=-2, pq=-15
得p=-5,q=3 或者p=3,q=-5
故p²+q²=9+25=34
p+q=-2, pq=-15 , p2+q2=(p+q)2-2pq=4+30=34
x2 +(p+q)x+pq=(x+p)(x+q)=(x-5)×(x+3)
则有p+q=-2
(x-5)(x+3)
=x2-5x+3x-15
=x2-2x-15
所以(p+q)=-2 pq=-15
p2+q2=(p+q)2-2pq
=(-2)(-2)-2(-15)
=34
平方都打成2了