1.
解:
(1)(2x-3y+7)+(6x-5y-2)=2x-3y+7+6x-5y-2=8x-8y+5.
(2)(a
-6a-7)-(a
-3a+4)=a
-6a-7-a
+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.
解:
(1)(4a
-3a)-(2a
+a-1)+(2-a
-4a)=4a
-3a-2a
-a+1+2-a
-4a=a
-8a+3.
当a=-2时,原式=(-2)
-8×(-2)+3=4+16+3=23.
(2)(ab-3a
)-2b
-5ab-(a
-2ab)=ab-3a
-2b
-5ab-a
+2ab=-4a
-2ab-2b
.
当a=1,b=-2时,原式=-4×1
-2×1×(-2)-2×(-2)^2=-4-(-4)-2×4=-4+4-8=-8.
3.
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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