
f(x+y,x-y)=x^2+y^2+e^xy,求f(x,y)
1个回答
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令u=x+y,v=x-y,则
x=(u+v)/2
y=(u-v)/2
故
f(x+y,x-y)=f(u,v)=[(u+v)/2]^2+[(u-v)/2]^2+e^[(u+v)/2*(u-v)/2]
=(u²+v²)/2+e^[(u²-v²)/4]
故
f(x,y)=(x²+y²)/2+e^[(x²-y²)/4]
x=(u+v)/2
y=(u-v)/2
故
f(x+y,x-y)=f(u,v)=[(u+v)/2]^2+[(u-v)/2]^2+e^[(u+v)/2*(u-v)/2]
=(u²+v²)/2+e^[(u²-v²)/4]
故
f(x,y)=(x²+y²)/2+e^[(x²-y²)/4]
追问
谢谢你!
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