# Proving Trig identities

1. May 15, 2010

### seastick

1. How do I prove sinxcosxsec^2x=tanx

2. Relevant equations
sec^2x = tan^2x + 1

3. The attempt at a solution

sinxcosx(tan^2x + 1)
tan^2xsinxcosx +sinxcosx
sin^2x/cos^2x*sinxcosx + sinxcosx - is this valid?

I'm not sure what I've done is even correct - but it doesn't seem to be going anywhere helpful?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. May 15, 2010

### The Chaz

Rewrite secant squared as 1/cos squared. The you'll have (sincos)/(coscos). Cancel cosines and you're done. I'll edit this from my computer and add arguments later!

3. May 15, 2010

### iRaid

secant = 1/cosine
cosecant = 1/sine
cotangent = 1/tangent

4. May 15, 2010

### The Chaz

SOHCAHTOA. qed

5. May 16, 2010

### seastick

6. May 16, 2010

### HallsofIvy

Staff Emeritus
Wasn't that Lewis and Clark's indian guide?

7. May 16, 2010

### The Chaz

No, this is the one that's featured on the new US coins ;)