Verified answer

x² + 24x - 11 = x² + 24x +144 - 144 - 11 = (x² + 2 * 12 * x + 12²) - 155 = (x + 12)²-155

3x² - 48x + 5 = 3(x² - 16x) + 5 = 3(x² - 16x + 64 - 64) + 5= 3[(x² - 16x + 64) -64] +  + 5 = 3[(x - 8)² - 64] + 5 = 3(x - 8)² - 192 + 5 = 3(x - 8)² - 187