1,已知a^2-b^2=20,a+b=-5,求a-b2已知：x-y=9xy=4,求x^2+y^23.x^2+2x+1=0求x^2+1/x^24.（a+b)^3=7(a-b)^2=4求a^2+b^2和ab

Question

1,已知a^2-b^2=20,a+b=-5,求a-b 2已知：x-y=9xy=4,求x^2+y^2
3.x^2+2x+1=0 求x^2+1/x^2
4.（a+b)^3=7(a-b)^2=4
求a^2+b^2和ab

Answer 1

1.
a²-b²=20
(a+b)(a-b)=20
a+b=-5代入
-5(a-b)=20
a-b=-4
2.
x-y=9xy=4
x-y=4 xy=4/9
x²+y²=(x-y)²+2xy
=4²+2×(4/9)
=152/9
3.
x²+2x+1=0
等式两边同除以x
x+2 +1/x=0
x+ 1/x=-2
x²+1/x²=(x+1/x)²-2=(-2)²-2=4-2=2
4.是不是你抄错题了,那个3次方应该是2次方.
(a+b)²=7 (a-b)²=4
a²+2ab+b²=7 (1)
a²-2ab+b²=4 (2)
(1)+(2)
2(a²+b²)=11
a²+b²=11/2
(1)-(2)
4ab=3
ab=3/4