(1)原式=-+3×2 =-+6 =-; (2)原式=(1-)(1+)-(12-4+1) =×(1-3)-12+4-1 =-2-12+4-1 =4-2-13; (3), ①+②×3得2x+9x=33, 解得x=3, 把x=3代入②得9-y=11, 解得y=-2, 所以方程组的解为; (4)原方程整理得 | 2(x+y)-3(x-y)=3① | 4(x+y)+3(x-y)=15② |
| | , ①+②得6(x+y)=18, 则x+y=3④, 把④代入①得6-3(x-y)=3, 则x-y=1⑤, ④+⑤得x=2,④-⑤得y=1, 所以原方程组的解为. |