# Thread: proving sin and cos identities

1. ## proving sin and cos identities

i'm not sure im doing this right and im having trouble understanding this lesson
what i have is:
$\cos\theta+\sin\theta \tan\theta = \displaystyle{\frac{1}{\cos\theta}}$
$\cos\theta+\sin\theta\displaystyle{\frac{\sin\thet a}{\cos\theta}}$
\cos\theta+\displaystyle{\frac{\sin^2\theta\}{\cos \theta}}
$\displaystyle{\frac{\cos^2\theta+\sin^2\theta}{\co s\theta}}$
which would give me the correct answer but im worried i've done something incorrectly with the fractions
also i'm kind of new to this latex thing, but the third line was giving me a syntax error and i don't know what i did wrong exactly so i took the tags off

2. Originally Posted by allywallyrus
i'm not sure im doing this right and im having trouble understanding this lesson
what i have is:
$\cos\theta+\sin\theta \tan\theta = \displaystyle{\frac{1}{\cos\theta}}$

$\cos\theta+\sin\theta\displaystyle{\frac{\sin\thet a}{\cos\theta}}$

$cos(\theta)+ \frac{sin^2(\theta)}{cos(\theta)}$

$\displaystyle{\frac{\cos^2\theta+\sin^2\theta}{\co s\theta}}$

which would give me the correct answer but im worried i've done something incorrectly with the fractions
also i'm kind of new to this latex thing, but the third line was giving me a syntax error and i don't know what i did wrong exactly so i took the tags off
Nope your maths is good, you just need to use the Pythagorean identity ( $sin^2(x) + cos^2(x) = 1$) to get to the final answer

3. oh good, thats what i was hoping to hear
and i dont suppose there is any rule against bumping this thread with new questions a little later on? i will probably have a couple more