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问题: 若设2008x^2=2007y^2,且1/x+1/y=1(x>0,y>0).

若设2008x^2=2007y^2,且1/x+1/y=1(x>0,y>0).求证根号(2008x+2007y)=根号2007+根号2008

解答:

2008x+2007y=2007y^2/x+2007y=2007y^2(1/x+1/y)=2007y^2
√(2008x+2007y)=√2007y

2008x^2=2007y^2
x>0,y>0,√2008*x=√2007*y,√2008=√2007*y/x
√2007+√2008=√2007+√2007*y/x=√2007(1+y/x)
1/x+1/y=1,y/x+1=y
√2007+√2008=√2007y

√(2008x+2007y)=√2007+√2008