Quick trigonometry question. Are you allowed to cross multiply to prove identities?

Question

amistre64 · Answer

generally you have to work one side to the other ... altering both sides at the same time is not a good approach.

ikram002p · Answer

Your allowed with caution for values that make denominator =0

amistre64 · Answer

cross multiplication, or working backwards is a good way to discover an approach to reach the solution tho.  but your proofing has to rely on the manipulation of one side into the other.

steve816 · Answer

For example:$$\frac{ \cos \theta }{ \cos \theta - \sin \theta } = \frac{ 1 }{ 1 - \tan \theta }$$

steve816 · Answer

Cross multiplying to prove this seems much easier.

amistre64 · Answer

just divide top and bottom by cos(t) ... right?

amistre64 · Answer

since tan(t) is not defined for cos(t)=0 anyways, then there is not discrepancy

ikram002p · Answer

Yeah showing cos t-sin t /cos = tan t -1 is easier

steve816 · Answer

oh wow, you're right I guess.

steve816 · Answer

Alright, thanks guys.