先化简再求值:(3x^2-xy+5)-(5xy-4x^2+5),其中x=2,y=1/3

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先化简再求值:(3x^2-xy+5)-(5xy-4x^2+5),其中x=2,y=1/3先化简再求值:(3x^2-xy+5)-(5xy-4x^2+5),其中x=2,y=1/3先化简再求值:(3x^2-x

先化简再求值:(3x^2-xy+5)-(5xy-4x^2+5),其中x=2,y=1/3
先化简再求值:(3x^2-xy+5)-(5xy-4x^2+5),其中x=2,y=1/3

先化简再求值:(3x^2-xy+5)-(5xy-4x^2+5),其中x=2,y=1/3
=3x^2-xy+5-5xy+4x^2-5
=7x^2-6xy
=7*2^2-6*2*1/3
=28-4
=24

(3x^2-xy+5)-(5xy-4x^2+5)
=3x^2-xy+5-5xy+4x^2-5
=3x^2+4x^2-xy-5xy+5-5
=7x^2-6xy
=7*2^2-6*2*1/3
=28-4
=24

原式=3x^2-xy+5-5xy+4x^2-5
=7x^2-6xy
然后自己带入就行了