Which of the following are identities? Check all that apply.
A. sinx+sin5x/cosx+cos5x=tan3x
B. sin8x=2sin4xcos4x
C. 1-tan^2x/2tanx=1/tan2x
D. (sinx-cosx)^2=1+sin2x

Question

Which of the following are identities? Check all that apply.
A. sinx+sin5x/cosx+cos5x=tan3x
B. sin8x=2sin4xcos4x
C. 1-tan^2x/2tanx=1/tan2x
D. (sinx-cosx)^2=1+sin2x

anonymous · Answer

@Hero @jim_thompson5910 @satellite73

anonymous · Answer

I feel like D is one right??

trojanpoem · Answer

A) Just assume a random number as simplifying it is overwhelming sin(3x+2x) etc..

sin1 + sin5/cos1+cos5 = 0.5 , tan3x = tan3 = 0.5

The identity is correct.

B -> OK
C -> OK

D) sin^2x + cos^2x - 2sinxcosx = 1 - sin2x (NO)

anonymous · Answer

OH!!! okay...i see what i did for d...i mixed it up with (sinx+cosx)^2....that would equal 1+sin2x!

anonymous · Answer

it is not (sinx-cosx)^2

anonymous · Answer

thank you! is Pre-calc your strong suit?? @TrojanPoem

trojanpoem · Answer

@ceceburns2010 , what do you mean ?

anonymous · Answer

like are you good at pre-calc??@TrojanPoem

trojanpoem · Answer

Sure.

trojanpoem · Answer

Hmm ?

anonymous · Answer

so...if i ever needed help with any pre-calc work...you would be the person i go to? or prob not? bc i see myself having a lot of questions in the future. :/

trojanpoem · Answer

Whenever you're stuck , tag me.

anonymous · Answer

awesome! Thanks! @TrojanPoem

trojanpoem · Answer

You're welcome.