x^2+7x-9=0?

0 ⤊

use complete the square method

2007-11-04 13:56:39 · 3 answers · asked by Jake 1 in Science & Mathematics ➔ Mathematics

3 answers

x² + 7x + 49/4 = 9 + 49/4
(x + 7/2)² = 85/4
x + 7/2 = ± √85 / 2
x = - 7/2 ± √85 / 2
x = (-1/2) (7 ± √85)

2007-11-04 20:21:35 · answer #1 · answered by Como 7 · 0⤊ 1⤋

xÂ² + 7x - 9 = 0

(a+b)Â² = aÂ² + 2ab + bÂ²
aÂ² = xÂ²
a = x

2ab = 7x
2bx = 7x
b = 7/2
bÂ² = 49/4

xÂ² + 7x + 49/4 - 85/4 = 0
(x+7/2)Â² = 85/4
(x+7/2) = Â±sqrt(85)/2
x = (-7Â±sqrt(85))/2

2007-11-04 22:05:42 · answer #2 · answered by gudspeling 7 · 0⤊ 0⤋

x2 + 7x - 9 = 0
x2 + 7x + 49/4 = 9 + 49/4
(x + 7/2)2 = 85/4
x + 7/2 = sqrt(85)/2
x = -7/2 +- sqrt(85)/2

2007-11-04 22:32:09 · answer #3 · answered by selang er uu 2 · 0⤊ 0⤋