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苏科版七年级下册数学书习题9.3答案

时间:2016-12-07 来源:书通网 共计4题

习题9.3第1题答案

解(1)(x-3)(2x+5)=2x2+5x-6x-15=2x2-x-15.

(2)(2a+1)(-a-2)=-2a2-4a-a-2=-2a2-5a-2.

(3)(x+1/2)(x-1/3)=x2-1/3x+1/2x-1/6=x2+1/6x-1/6.

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(5)(xy+1)(xy-4)=x2y2-4xy+xy-4=x2y2-3xy-4.

(6)(5m-4n)(4m-5n)=20m2-25mn-16mn+20n2=20m2-41mn+20n2.

习题9.3第2题答案

解:(1)(2a-b)(a+2b-3)=2a2+4ab-6a-ab-2b2+3b=2a2+3ab-6a+3b-2b2;

(2)(x+y+5)(x+y+4)=[(x+y)+5][(x+y)+4]=(x+y)2+9(x+y)+20=x2+xy+xy+y2+9x+9y+20=x2+2xy+9x+9y+y2+20.

习题9.3第3题答案

解:(x-1)(2x+1)-2(x-5)(x+2)=2x2-x-1-2(x2-3x-10)=2x2-x-1-2x2+6x+20=5x+19.当x=1/5时,5x+19=5×1/5+19=20.

习题9.3第4题答案

解:(90+a)(60+a)-90×60=90×60+90a+60a+a2-90×60=(a2+150a)(cm2).

答:它的面积将增加(a2+150a)cm2.

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