18. b) E(x) = 4x² - 4x - 1 = (2x - 1)² -2 (2x -1)² ≥ 0 ptr.(2x-1)² = 0 E ≥ -2
c) E(x) = 9x² - 6x + 3 = (3x-1)² +2 (3x-1)² ≥ 0 ptr,(3x-1)² = 0 E ≥ 2
19.b) 1 - x² - x = 2 - (x² + x + 1) = 2 - [(x+1/2)² + 3/4] = 5/4 - (x+1/2)²
(x+1/2)≥ 0 ⇒ E(x) ≤ 5/4
c) -x² + 6x - 4 = 5 - (x -3)² (x - 3) ≥ 0 E(x) ≤ 5
