SOLUTION: find the zeroes: f(x) = x^4+x^2-20

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Question 699419: find the zeroes:
f(x) = x^4+x^2-20
Found 2 solutions by stanbon, MathLover1:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
find the zeroes:
f(x) = x^4+x^2-20
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Solve:
x^4 + x^2 - 20 = 0
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Factor:
(x^2+5)(x^2-4) = 0
---
x = +-sqrt(5) or x = +-2i
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Cheers,
Stan H.
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Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!
f%28x%29+=+x%5E4%2Bx%5E2-20......replace x%5E2 with 5x%5E2-4x%5E2
f%28x%29+=+x%5E4%2B5x%5E2-4x%5E2-20..group
f%28x%29+=+%28x%5E4%2B5x%5E2%29-%284x%5E2%2B20%29
f%28x%29+=+x%5E2%28x%5E2%2B5%29-4%28x%5E2%2B5%29
f%28x%29+=+%28x%5E2-4%29++%28x%5E2%2B5%29
f%28x%29+=+%28x-2%29+%28x%2B2%29+%28x%5E2%2B5%29
solutions:
+%28x-2%29+%28x%2B2%29+%28x%5E2%2B5%29=0
if +x-2=0...=>...+x=2
if +x%2B2=0...=>...+x=-2
if +x%5E2%2B5=0...=>...+x%5E2=-5...=>...+x=sqrt%28-5%29...=>...+x=2.24i or +x=-2.24i

+graph%28+600%2C+600%2C+-5%2C+5%2C+-30%2C+10%2C+x%5E4%2Bx%5E2-20%29+