syx1967
春芽
共回答了11个问题采纳率:90.9% 举报
由于x / y = 1 / 3,即 y=3 x ;
化简3x ^2-3y ^2 / x ^2+2xy+y ^2
= 3(x ^2 - y ^2) / (x + y)^2
= 3( x+y )( x-y ) / ( x+y )( x+y )
= 3( x-y ) / ( x+y )
将 y=3x 代入,得
原式 = 3( x-3x ) /( x+3x )
= 3× (-2x) / 4x
= -6x / 4x
= -3/2
1年前
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