Question

谁来帮我做一下几个一元一次方程的题啊啊、、

(1) 2（3xy-2x²-3y²)+3(x²-5xy+3y²)
(2) 3(x²-2x+1)-4(2x²-x-3)
(3) -(-a²+2ab+5²)+(-a²-ab+b²），其中a=1/30，b=20

谢谢

Answer 1

(1) 2（3xy-2x²-3y²)+3(x²-5xy+3y²)
= 6xy-4x²-6y²+3x²-15xy+9y²
= 6xy-15xy-4x²+3x²+9y²-6y²
=-9xy-x²+3y²

(2) 3(x²-2x+1)-4(2x²-x-3)
= 3x²-6x+3-8x²+4x+12
= 3x²-8x²-6x+4x+3+12
= -5x²-2x+15

(3) -(-a²+2ab+5²)+(-a²-ab+b²），其中a=1/30，b=20
=a²-2ab-5²-a²-ab+b²
=a²-a²-2ab-ab+b²-5²
=-3ab+b²-25
=-3*1/30*20+20²-25
=-2+400-25
=373

Answer 2

(1) 2（3xy-2x²-3y²)+3(x²-5xy+3y²)
=6xy-4x²-6y²+3x²-15xy+9y²
=-x²-9xy+3y²
(2) 3(x²-2x+1)-4(2x²-x-3)
=3x²-6x+3-8x²+4x+12
=-5x²-2x+15
(3) -(-a²+2ab+5b²)+(-a²-ab+b²）
=a²-2ab-5b²-a²-ab+b²
=-3ab-4b²
=-3×1/30×20-4×20²
=-2-1600
=-1602

Answer 3

-x2-9xy+3y2
-5x2-2x+12
377