exam coming up...need some help with these identities for practise.(adsbygoogle = window.adsbygoogle || []).push({});

prove the following:

A)

[tex]\frac{tan^3x}{1+tan^2x}+\frac{cot^3x}{1+cot^2x}=\frac{1-2sin^2xcos^2x}{sinxcos}[/tex]

B)

[tex]sec^6x-tan^6x=1+3tan^2xsec^x[/tex]

C)

[tex]cos^4x=\frac{3}{8}+\frac{1}{2}cos2x+\frac{1}{8}cos4x[/tex]

D)

[tex]cos\frac{x}{2}=\pm\sqrt{\frac{1+cosx}{2}}[/tex]

i tried really hard but can't seem to get any progress. i tried to get common denominator, use other identies to transform but nothing, can i get some advice on what method to use or where to start?

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# Proving trig identities

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