Question

Find the zeros of y = x2 - 4x - 9 by completing the square.
ОА. x = -2 + 13
OB. х = 3+ (113
ос. х = 2+ (13
OD. х = +3

Answer 1

${x}^{2} - 4x - 9 = 0 \\ d = {( - 4)}^{2} - 4 \times ( - 9) = 52 = (2 \sqrt{13} ) ^{2} \\ x = \frac{4 + 2 \sqrt{13} }{2} = 2 + \sqrt{13} \\ x = \frac{4 - 2 \sqrt{13} }{2} = 2 - \sqrt{13}$

Zeros of function:

2+_/13

2-_/13