SOLUTION: i do not understand how x^4-9x^2 equals 20

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Question 854182: i do not understand how x^4-9x^2 equals 20
Found 2 solutions by richwmiller, josgarithmetic:
Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
Who said it does?

Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
x%5E4-9x%5E2=20

The equation is in quadratic form.
x%5E4-9x%5E2-20=0 which seems not factorable.

Let v=x^2 and first solve for v.
v%5E2-9v-20=0
Discriminant is 9%2A9-4%28-20%29=81%2B80=161 and 161=7%2A23.
v=%289%2B-+sqrt%28161%29%29%2F2
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Remember how v was assigned and substituted.
highlight%28x=0%2B-+sqrt%28%289%2B-+sqrt%28161%29%29%2F2%29%29, which is itself four different expressions, four different values.


* The zero is included only to allow for rendering; it can otherwise be omitted.