#If tan^4a + tan^2a = 1#, then find the value of #cos^4a + cos^2a ?#

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Answer 1 · 2016-12-26T08:38:25

Given

#tan^4a+tan^2a=1#

#=>(tan^2a+1)tan^2a=1#

#=>sec^2atan^2a=1#

#=>(1/cos^2a)tan^2a=1#

#=>tan^2a=cos^2a#

#=>sin^2a/cos^2a=cos^2a#

#=>sin^2a=cos^4a#

#=>1-cos^2a=cos^4a#

#=>cos^4a+cos^2a=1#