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苏科版七年级上册数学书习题3.6答案

1习题3.6第1题答案

(1)(2x-3y+7)+(6x-5y-2)

=2x-3y+7+6x-5y-2

=8x-8y+5          

(2)(a2-6a-7)-(a2-3a+4)

=a2-6a-7-a2+3a-4

=-3a-11          

(3)(7x+2y)+(4+3x)-(15y-7)

=7x+2y+4+3x-15y+7

=10x-13y+11           

(4)5(x+y)-4(3x-2y)-3(2x-3y)

=5x+5y-12x+8y-6x+9y

=-13x+22y

2习题3.6第2题答案

(1)(4a2-3a)-(2a2+a-1)+(2-a2-4a)

=4a2-3a-2a2-a+1+2-a2-4a

=a2-8a+3

当a=-2时,

原式=(-2)2-8×(-2)+3 

= 4+16+3 

= 23            

(2)(ab-3a2)-2b2-5ab-(a2-2ab)

=ab-3a2-2b2-5ab-a2+2ab

=-4a2-2ab-2b2

当a=1,b=-2时,

原式=-4×12-2×1×(-2)-2×(-2)2

=-4-(-4)-2×4

=-4+4-8

=-8

3习题3.6第3题答案

解:(1)A,D两站的距离为

a+b+(3a+2b)

=a+b+3a+2b

=4a+3b         

(2)C,D两站的距离为

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

=3a+2b-2a+b

=a+3b

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