SOLUTION: b^4 + 13b^2 + 36 = 0

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Question 200825: b^4 + 13b^2 + 36 = 0
Answer by RAY100(1637) About Me  (Show Source):
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b^4 +13b^2 +36 =0
let a = b^2
a^2 +13a +36 =0
(a+9)(a+4) =0
subst back
(b^2 +9)(b^2 +4) =0
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b^2 +9 =0,,,,, b^2 = -9,,,b= +/- 3i
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b^2 +4 = 0,,,,,,b^2 = -4,,,,,,,,,b= +/- 2i