Question

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Answer 1

sec^2 theta = what ?
look at the identities :-)

Answer 2

yeah

Answer 3

sec^2x= 1+ tan^2x
here are
http://prntscr.com/77xqcf
trig identities
so replace sec^2x by 1+tan^2x

Answer 4

-tag2x+sec2x=1
-(senx+cosx)2+(1/cosx)2=1
-(sen2x/cos2x)+(1/cos2x)=1
-sen2x+1/cos2x=1
-sen2x+1=cos2x
Cos2x+sen2x=1 pythagorean

Answer 5

it is not that hard
just 2 step :-)