Giải tốn sau phương pháp hình học 1) f ( x1 , x2 ) = x1 + x2 → 3 x1 + x2 ≤ 2 x1 − x2 ≥ x ≥ 0, x ≥ (1) (2) 2) f ( x1 , x2 ) = x1 + x2 → max x1 + x2 ≤ 2 x1 − 3x2 ≥ −3 x ≥ 0, x ≥ (1) (2) 3) f ( x1 , x2 ) = x1 + x2 → max 3x1 + x2 ≤ 12 3x1 + x2 ≤ x ≥ 0, x ≥ (1) (2) 4) f ( x1 , x2 ) = x1 + 3x2 → max x1 + x2 ≤ 12 3x1 + x2 ≤ 12 x ≥ 0, x ≥ (1) (2) 5) f ( x1 , x2 ) = − x1 + x2 → min(max) − x1 − x2 ≤ x − 2x ≤ − x1 + x2 ≤ x1 ≥ 0, x2 ≥ (1) (2) (3) 6) f ( x1 , x2 ) = x1 − x2 → max 4 x1 + x2 ≥ 12 − x + x ≤ x1 + x2 ≤ x1 ≥ 0, x2 ≥ (1) (2) (3) 7) f ( x1 , x2 ) = − x1 + x2 → max x1 − x2 ≤ 20 − x1 + x2 ≤ 12 x ≥ 0, x ≥ (1) (2) 8) f ( x1 , x2 ) = − x1 + x2 → 4 x1 + x2 ≤ 20 x − 3x ≤ − x1 + x2 ≤ x1 ≥ 0, x2 ≥ (1) (2) (3) 9) f ( x1 , x2 ) = x1 − x2 → max x1 + x2 ≤ x − 3x ≤ x2 ≤ x1 ≥ 0, x2 ≥ (1) (2) (3) 10) f ( x1 , x2 ) = −2 x1 − x2 → x1 + x2 ≤ x + x ≥ x1 − x2 ≥ x1 ≥ 0, x2 ≥ (1) (2) (3) -TTTN -