几道简单的整式计算,尽量写清楚一点计算:(1-x)(0.6-x)(2x+y)(x-y)(2n+5)(n-3)(ax+b)(cx+d)化简(x-y)(x-2y)- (1/2) (2x-3y)(x+2y),并求出当x=2,y=5时的值
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原式=0.6-x-0.6x+x2
=x2-1.6x+0.6
原式=2x2-2xy+xy-y2
=2x2-xy-y2
原式=2n2-6n+5n-15
=2n2-n-15
原式=acx2+adx+bcx+bd
=acx2+(ad+bc)x+bd
原式=(x2-2xy-xy+2y2)-(1/2)(2x2+4xy-3xy-6y2)
=(x2-3xy+2y2)-(1/2)(2x2+xy-6y2)
=x2-3xy+2y2-x2-(1/2)xy+3y2
=-(7/2)xy+5y2
将x=2,y=5带入得：-(7/2)*2*5+5*5*5
=90======以下答案可供参考======
供参考答案1:
(1)0.6-1.6x+x^2
(2)2x^2-xy-y^2
(3)2n^2-n-15
(4)acx^2+(ad+bc)x+bd
(5)原式=(x^2-3xy+2y^2)-(1/2) (2x^2+xy-6y^2)
=-(7/2)xy+5y^2
当x=2, y=5时,原式=-(7/2)*2*5+5*5^2
=90供参考答案2:
(1-x)(0.6-x)
=0.6-X-0.6X+X^
=X^-(1+0.6)X+0.6
=X^-1.6X+0.6
(2x+y)(x-y)
=2x^-2xy+xy-y^=2x^-(2-1)xy-y^=2x^-xy-y^(2n+5)(n-3)
=2n^-6n+5n-15=2n^-(6-5)n-15=2n^-n-15(ax+b)(cx+d)
=ax^+adx+bcx+bd=ax^+(ad+bc)x+bd(x-y)(x-2y)- (1/2) (2x-3y)(x+2y)=[2(x-y)(x-2y)- (2x-3y)(x+2y)]/2=(2x^-2xy-xy+2y^-2x^-4xy+3xy+6y^)/2=[(-2-1-4+3)xy+6y^]/2=(-4xy+6y^)/2=[2(3y^-2xy)]/2=3y^-2xy把x=2, y=5的值代入上式3y^-2xy=3*5*5-2*2*5=75-20=55