SOLUTION: I need help in this problem. {{{-2x^2=72}}} The answers are as given a. x= +or-36 b. x=+or-6 c. x=+or-36i d. x=+or-6i

Algebra ->  College  -> Linear Algebra -> SOLUTION: I need help in this problem. {{{-2x^2=72}}} The answers are as given a. x= +or-36 b. x=+or-6 c. x=+or-36i d. x=+or-6i      Log On


   

Question 548232: I need help in this problem.
-2x%5E2=72
The answers are as given
a. x= +or-36
b. x=+or-6
c. x=+or-36i
d. x=+or-6i
Answer by mathie123(224) About Me  (Show Source):
You can put this solution on YOUR website!
-2x%5E2=72
Divide both sides by -2 to get:
-2x%5E2%2F-2=72%2F-2
x%5E2=-36
Take the square root of both sides to get:
x=%2Bsqrt%28-36%29
or
x=-sqrt%28-36%29
Now we know that sqrt%28-1%29=i by definition
x=%2Bsqrt%28-1%2A36%29
or
x=-sqrt%28-1%2A36%29

x=%2Bsqrt%28-1%29%2Asqrt%2836%29
or
x=-sqrt%28-1%29%2Asqrt%2836%29
x=%2Bi%2Asqrt%2836%29
or
x=-i%2Asqrt%2836%29
x=%2Bi%2A6
or
x=-i%2A6
(Which is answer d)