七年级数学下册第九章习题答案
初一课程繁多，任务加重，同学们要如何准备呢?接下来是小编为大家带来的七年级数学下册第九章习题答案，供大家参考。
七年级数学下册第九章习题答案：
习题9.1第1题答案
习题9.1第2题答案
习题9.1第3题答案
习题9.2第1题答案解：(1)1/2ab2•(2a2b-3ab2)=1/2ab2•(2a2b)+1/2ab2•(-3ab2)=a3b3-3/2a2
(2)x(2x-5)+3x(x+2)-5x(x-1)=2x2-5x+3x2+6x-5x2+5x=6x.
(3)a(a2+ab+b2)-b(a2+ab+b2)=a3+a2b+ab2-a2b-ab2-b3=a3-b3.
(4)原式=a3-3a+a3+3a2-3a3+3a=-a3+6a2.
习题9.2第2题答案解：因为A=-2ab,B=4ab(a-b)=4a2b-4ab2,所以A•B=-2ab(4a2b-4ab2)=-8a3b2+8a2b3.
习题9.2第3题答案(1)-6ab (2)2a (3)2ab 5b2 (4)1 4ab 8a2b2
习题9.2第4题答案解：(a+b)(c+d)=(a+b)•c+(a+b)•d=ac+bc+ad+bd.
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.
(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.
习题9.4第1题答案(1)4a2+12ab+9b2
(2)16x2-40xy+25y2
(3)1/3a2-2ab+3b2
(4)a2+4ab+4b2
习题9.4第2题答案解：草坪的面积可表示为S=20×20-20•a-20•a+a2，也可表示为S=(20-a)(20-a).得到等式(20-a)2=400-40a+a2.说明：草坪的面积S=20×20-20•a-20•a+a2=400-40a+a2.
习题9.4第3题答案
习题9.4第4题答案(1)4m2-9n2 (2)4a2-25b2 (3)4-9x2 (4)y2-1/9x2
习题9.4第5题答案解：(1)9982=(1000-2) 2=10002-2×1000×2+22=1000000-4000+4=996004.
(2)1007×993=(1000+7)(1000-7)=10002-72=1000000-49=999951.
习题9.4第6题答案解：(1)(x-y) 2-x2-2xy+y2-(x2+2xy+y2)-(x2+2xy+y2)=-4xy.
(2)(3a-b) 2+(b+3a) 2=9a2-6ab+b2+b2+6ab+9a2=18a2+2b2.
(5)4(a+2) 2-7(a+3)(a-3)+3(a-1) 2=4(a2+4a+4)-7(a2-9)+3(a2-2a+1)=4a2+16a+169-7a2+63+3a2-6a+3=10a+82.
(6)(2a-b-3)(2a+b+3)=[(2a-3)-b][(2a-3)+b]=(2a-3) 2-b2=4a2-12a+9-b2.
习题9.4第7题答案解：(1)原式=24y+18，当y=0.4时，原式=27.6.
(2)原式=5ab，当a=7/15，b=3/14时，原式=1/2 .
习题9.5第1题答案解：(1)ap-aq+am=a(p-q+m).
(2)4x2-8xy+2x=2x(2x-4y+1).
(3)12xyz-9x2y=3xy(4z-3x).
(5)6a2b-9ab2+15ab=3ab(2a-3b+5).
习题9.5第2题答案解：(1)4ab(2x-y)+b(2x-y)=b(2x-y)(4a+1);
(2)6a(1-b) 2-2(b-1) 2=2(b-1) 2•(3a-1).
习题9.5第3题答案解：(1)1-16a2=(1+4a)(1-4a);
(2)m2-9n2=(m+3n)(m-3n);
(3)4x2-81y2=(2x) 2-(9y2)=(2x+9y)(2x-9y);
(4)9a2x2-b2y2=(3ax+by)(3ax-by).
习题9.5第4题答案解：(1)(x+5) 2-4=(x+5) 2-22=(x+5+2)(x+5-2)=(x+7)(x+3);
(2)(a+b) 2-a2=(a+b+a)(a+b-a)=b(2a+b);
(3)(a2+b2)2-a2b2=(a2b2+ab)(a2b2-ab);
(4)49(a-b)2-16(a+b)2
=[7(a-b)] 2-[4(a+b)] 2
=[7(a-b)+4(a+b)][7(a-b)-4(a-b)]
=(7a-7b+4a+4b)(7a-7b-4a-4b)
=(11a-3b)(3a-11b).
习题9.5第5题答案解：(1)a2b2-2ab+1=(ab-1)2;
(2)9-12a+4a2=(2a-3)2;
(3)4x2+4x+1=(2x+1)2;
(4)x2-6xy+9y2=(x-3y)2.
习题9.5第6题答案解：(1)(a+b)2+6(a+b)+9=(a+b+3)2;
(2)16-24(x-y)+9(x-y)2=[3(x-y)-4]2=(3x-3y-4)2;
(3)a2-2a(b+c)+(b+c)2=[a-(b+c)]2=(a-b-c)2;
(4)4x2-4x(y-1)+(y-1)2=[2x-(y-1)]2=(2x-y+1) 2.
习题9.5第7题答案解：(1)-a+2a2-a3=-a(1-2a-22)=-a(a-1)2;
(2)3ax2-3ay2=3a(x2-y2)=2a(x+y)(x-y);
(3)16a2b-13a2-4ab2=-4a(4a2-4ab+b2)=-4a(2a-b) 2;
(4)x2(y2-1)+(1-y2)=(y2-1)(x2-1)=(y+1)(y-1)(x+1)(x-1).
习题9.5第8题答案
