# Homework Help: Trig help

1. Oct 31, 2005

### gator

Ive been given very little notes from my teahcer, and cant do these. looked online, but its was no use.

1. Using the identities to find the vales of each expression (no calc.)
(i) sin t = 15/17 , cos t = 8/17 find remaining trig functions
(ii) sec^2 Pie/12 - tan^2 Pie/12

2. Find exact value
(i) tan* = -3 , cos *>0

3.Use reference angles to find exact value (no calc.)
(i) cos 225*
(ii) sin ( -pie/6 )

Thanks a bunch!

2. Oct 31, 2005

### TenaliRaman

1.(i) Hint : 15^2 + 8^2 = 17^2
1.(ii) Hint : cos^2(x) = 1 - sin^2(x)
Divide throughout by [something] to get tan^2(x)

2.(i) ugly problem
use my hint for 1.(ii), you may not get exact angle though i am afraid

3.(i) Hint : 225 = 180 + 45
3.(ii) Hint : Think what about what i did in 3.(i)

-- AI

3. Oct 31, 2005

### verty

Remember these three identities:

sin^2 + cos^2 = 1
sec^2 = 1 + tan^2
cosec^2 = 1 + cot^2

Learn them, be able to recite them.

One more thing, 2.(i) doesn't say 'no calc', so you can use your calculator there. What do the signs mean?

Last edited: Oct 31, 2005
4. Oct 31, 2005

### mathman

For (i), use definitions sec=1/cos, csc=1/sin, tan=sin/cos, cot=cos/sin.

5. Nov 7, 2005

### ryguy66

I'm having trouble proving these trig identities:
1. sinB+cosBcotB = cscB
2. (sinA/1-cosA)-cotA = cscA
3. 2tan13X/1+tan^2 13X = sin26X
4. secX-tanX/cscX-1 = tanX

6. Nov 8, 2005