SOLUTION: x^4+3x^2-28=0

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Question 579927: x^4+3x^2-28=0
Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
Factoring we get
x%5E4%2B3x%5E2-28=0 --> %28x%5E2%2B7%29%28x%5E2-4%29=0
If you do not "see"" that factoring make the change of variable y=x%5E2
to get y%5E2%2B3y-28=0. Then you can factor or apply the quadratic formula to find the roots, and hence the factors.
%28x%5E2%2B7%29%28x%5E2-4%29=0 --> %28x%5E2%2B7%29%28x%2B2%29%28x-2%29=0
x%5E2%2B7=0 does not yield any real roots. The real roots come from making zero the other 2 factors:
highlight%28x=-2%29 and highlight%28x=2%29