How do you solve #x^2 – x – 2 = 0#?

Question

25481 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2015-08-01T22:31:03

Solve y = x^2 - x - 2 = 0

Answer: -1 and 2.

Since (a - b + c = 0), use the shortcut. The 2 real roots are:
-1 and (-c/a = 2/1 = 2)

REMINDER of Shortcut.

When (a + b + c = 0) --> 2 real roots -> 1 and (c/a)

When (a - b + c = 0) --> 2 real roots --> (- 1) and (- c/a).

Try to remember this Shortcut. It will save you a lot of time and effort!!!.

Answer 2 · 2015-08-02T14:25:49

#x=-1, 2#

#x^2-x-2# is in the form of a quadratic equation, #ax+bx+c#, where #a=1, b=-1, and c=-2#. The quadratic formula can be used to solve this problem.

Quadratic Formula

#x=(-b+-sqrt(b^2-4ac))/(2a)# =

#x=(-(-1)+-sqrt((-1)^2-4*1*-2))/(2*1)# =

#x=(1+-sqrt(1+8))/2# =

#x=(1+-sqrt9)/2# =

#x=(1+-3)/2#

Solve for #x#.

#x=(1+3)/2=4/2=2#

#x=(1-3)/2=-2/2=-1#