SOLUTION: I have to solve this equation by making appropriate substitutions: x^4- 9x^2 = -20

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Question 848794: I have to solve this equation by making appropriate substitutions:
x^4- 9x^2 = -20
Answer by fcabanski(1391) About Me  (Show Source):
You can put this solution on YOUR website!
x%5E4-+9x%5E2+%2B20=0


Substitute u=x%5E2


u%5E2+-9u+%2B+20+=+0
(u-4)(u-5) = 0


u = 4 or 5


x%5E2+=+4 so x = + or - 2


x%5E2+=+5 so x = + or - sqrt%285%29