求解下列线性规划问题: (1)max z=x 1 +2x 2 , s.t.2x 1 +x 2 ≤8, -x 1 +x 2 ≤4, x 1 -x 2 ≤0, 0≤x 1 ≤3,x 2 ≥0; (2)min f=-3x 1 -11x 2 -9x 3 +x 4 +29x 5 , s.t.x 2 +x 3 +x 4 -2x 5 ≤4, x 1 -x 2 +x 3 +2x 4 +x 5 ≥0, x 1 +x 2 +x 3 -3x 5 ≤1, x 1 无符号限制,x i ≥0(j=2,3,4,5); (3)max x=x 1 +6x 2 +4x 3 , s.t.-x 1 +2x 2 +2x 3 ≤13, 4x 1 -4x 2 +x 3 ≤20, x 1 +2x 2 +x 3 ≤17, x 1 ≥1,x 2 ≥2,x 3 ≥3.