What are the solutions of the equation #9x^4-2x^2-7=0#?

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What are the solutions of the equation #9x^4-2x^2-7=0#?

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Answer 1 · 2018-06-02T08:11:15

#x_{1,2}=pm1#

Explanation:

Writing
#x^4-2/9x^2-7/9=0#
and substituting
#x^2=t#
we get
#t^2-2/9t-7/9=0#
so
#t_1=1/9+8/9=1#
#t_2=-7/9<0#( which is impossible!)
so
#x^2=1#
#x_1=1#
#x_2=-1#

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What are the solutions of the equation #9x^4-2x^2-7=0#?

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