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北师大版八年级下册数学书第四章复习题答案

时间:2016-12-10 来源:书通网 共计17题

第四章复习题第1题答案

(1)7x2-63

=7(x2-9)

=7(x+3)(x-3)

(2)a3-a

=a(a2-1)

=a(a+1)(a-1)

(3)3a2-3b2

=3(a2-b2

=3(a+b)(a-b)

(4)y2-9(x+y)2

=(y-3x-3y)(y+3x+3y)

=-(3x+2y)(4y+3x)

(5)a(x-y)-b(y-x)+c(x-y)=(x-y)(a+b+c)

(6)x(m+n)-y(n+m)+(m+n)=(m+n)(x-y+1)

(7)(x+y)2-16(x-y)2

=(x+y-4x+4y)(x+y+4x-4y)

=(5y-3x)(5x-3y).

(8)a2(a-b)2-b2(a-b)2

=(a-b)2(a2-b2

=(a-b)2(a+b)(a-b)

=(a-b)3(a+b)

(9)(x+y+z)2-(x-y-z)2

=(x+y+z- x+y+z)(x+y+z+ x-y-z)

=2(y+x)×2x

=4x(y+z)

(10)(x+y)2-14(x+y)+49=(x+y-7)2

第四章复习题第2题答案

(1)a2b2-0.01

=(ab)2-(0.1)2

=(ab+0.1)(ab-0.1)

(2)x2y-2xy2+y3

=y(x2-2xy+y2

=y(x-y)2

(3)16-(2a+3b)2

=[4+(2a+3b)][4-(2a+3b)]

=(4+2a+3b)(4-2a-3b)

(4)(a2+4)2-16a2

=(a2+4+4a)(a2+4-4a)

=(a+2)2(a-2)2

(5)x2-xy+1/4y2=(x-1/2y)2

(6)a2x2+16ax+64=(ax+8)2

(7)a4-8a2b2+16b4

=(a2-4b22

=[(a+2b)(a-2b)] 2

=(a+2b)2(a-2b)2

(8)9+6(a+b)+(a+b)2=(a+b+3)2

第四章复习题第3题答案

(1)原式=(3x+2y)2,当x=4/3,y=-1/2时

原式=[3×4/3+2×(-1/2)] 2=(4-1)2=9.

1.jpg

当a=-1/8,b=2时,原式=-1/8×2=-1/4

第四章复习题第4题答案

(1)2x2+2x+1/2

=2(x2+x+1/4)

=2(x+1/2)2

(2)(x+1)(x+2)+1/4

=x2+3x+2+1/4

=x1/4+3x+9/4

=(x+3/2)2

第四章复习题第5题答案

因为:257-512

=52×7-52×6

=(572-(562

=(57+56)(57-56

=56×6×56×4

=120×511

所以能被120整除

第四章复习题第6题答案

1/2x2+xy+1/2y2

=1/2(x2+2xy+y2

=1/2(x+y)2

当x+y=1时

原式=1/2(x+y)2=1/2

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