Answer: B
Explanation:
ax² + bx + c = 0 is rewritten as x² + (b/a)x + (b/2a)² = -c/a + (b/2a)²
A) 4x² + 9x + 5 = 0 --> x² + (9/4)x + (9/8)² = -5/4 + (9/8)²
= x² + (9/4)x + 81/64 = -5/4 + 81/64
B) 4x² + 12x + 7 = 0 --> x² + (12/4)x + (12/8)² = -7/4 + (12/8)²
= x² + 3x + 9/4 = -7/4 + 9/4 <---- this works!
C) 3x² - 6x - 4 = 0 --> x² + (-6/3)x + (-6/6)² = 4/3 + (-6/6)²
= x² - 2x + 1 = 4/3 + 1
D) 2x² - 8x - 9 = 0 --> x² + (-8/2)x + (-8/4)² = 9/2 + (-8/4)²
= x² - 4x + 4 = 9/2 + 4