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

Question

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

Answer 1

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