Question

X² - 7x-18 = 0

What is the set of all values of x that satisfy the equation above?
A. (-9,2)
B. (-6, 3)
C. (6, 3)
D. (9,-2)​

Answer 1

method 1.

`{x}^(2) - 7x - 18 = 0`

simplify:

`(x - 9)(x + 2) = 0`

so the answer is (D) x =9 or x = -2

method 2.

if

`{a}^(2)x+ bx + c = 0`

`x = \frac{ - b + \sqrt{ {b}^(2) - 4ac} }{2a} \: or \: \frac{ - b - \sqrt{ {b}^(2) - 4ac} }{2a}`

so

`x = \frac{ - ( - 7) + \sqrt{ { - 7}^(2) - 4(1)(18)} }{2(1)} or\frac{ - ( - 7) - \sqrt{ { - 7}^(2) - 4(1)(18)} }{2(1)}`

`x = ( 7 + √( 121 ) )/(2)or( 7 - √( 121 ) )/(2)`

`x = 9 \: \: \: \: or - 2`