x²-y²=55,x-y=5,则x+y=1.x²-y²=55,x-y=5,则x+y=2.已知x-y=1,x²+y²=25,则xy=3.若m（3x-y²）=y^4-9x²,则m=4.已知：x+y=9,xy=20,则x²+y²=,(x-y)²=说明理

Question

x²-y²=55,x-y=5,则x+y=
1.x²-y²=55,x-y=5,则x+y=________
2.已知x-y=1,x²+y²=25,则xy=___________
3.若m（3x-y²）=y^4-9x²,则m=___________
4.已知：x+y=9,xy=20,则x²+y²=___,(x-y)²=_____
说明理由~

Answer 1

1.x²-y²=55,x-y=5,则x+y=x²-y²/(x-y)=11
2.已知x-y=1,x²+y²=25,则xy=(x²+y²-(x-y)^2)/2=12
3.若m（3x-y²）=y^4-9x²,则m=y^4-9x²/（3x-y²）=-(3x+y^2)=-3x-y²
4.已知：x+y=9,xy=20,则x²+y²=(x+y)^2-2xy=41(x-y)²=(x+y)^2-4xy=1