Posted by **Deepa** on Sunday, February 17, 2013 at 10:06am.

Proving identities:

1) 1+ 1/tan^2x = 1/sin^2x

2) 2sin^2 x-1 = sin^2x - cos^2x

3) 1/cosx - cosx = sin x tan x

4) sin x + tan x =tan x (1+cos x)

5) 1/1-sin^2x= 1+tan^2 x

How in the world do I prove this...please help...

I appreciateyour time thankyou soo much!!

- Trig Identities -
**Reiny**, Sunday, February 17, 2013 at 10:24am
There is on one correct and foolproof way to prove identities.

There are some general rules you might follow

1. look for obvious relations , like sin^2 x + cos^2 x = 1

or 1 + tan^2 x = sec^2 x

-- make yourself a summary of these collected from your text or notebooks

2. usually, changing all ratios to sines and cosines often gives quick and easy results

3. start with the more complicated looking side, and try to work it towards the expression on the other side , or

4. work down one side until you can't seem to go any further, now switch to the other side and try to obtain that last expression

e.g. #4

sinx + tanx = tanx (1+cosx)

LS = sinx + sinx/cosx

= (sinxcosx + sinx)/cosx

= sinx(cosx + 1)/cosx

= (sinx/cosx)(1 + cosx)

= tanx (1 + cosx)

= RS

#2

2sin^2 x - 1 = sin^2x - cos^2x

RS = sin^2 x - (1 - sin^2 x)

= sin^2 x - 1 + sin^2 x

= 2sin^2 x - 1

= LS

well, that was an easy one

try the others by using similar methods.

come back if you get stuck.

- small correction - Trig Identities -
**Reiny**, Sunday, February 17, 2013 at 10:25am
My first line should have been:

There is NO one correct and foolproof way to prove identities.

- Trig Identities -
**Deepa**, Sunday, February 17, 2013 at 12:48pm
OHHH!!! Ok thankyou soooo much I greatly appreciate your help and one compliment...Your way better than my teacher...once again thankyou sooo much I think I get the jist of it now:)

## Answer this Question

## Related Questions

- Trigonometry - Prove the following trigonometric identities. please give a ...
- Trig - Given: cos u = 3/5; 0 < u < pi/2 cos v = 5/13; 3pi/2 < v < ...
- Mathematics - Trigonometric Identities - Let y represent theta Prove: 1 + 1/tan^...
- precalculus - For each of the following determine whether or not it is an ...
- Trig....... - I need to prove that the following is true. Thanks (2tanx /1-tan^x...
- Trig Identities - Prove the following identities: 13. tan(x) + sec(x) = (cos(x...
- Trigonometry - Please review and tell me if i did something wrong. Find the ...
- TRIG.............. - Q.1 Prove the following identities:- (i) tan^3x/1+tan^2x + ...
- trig 26 - simplify to a constant or trig func. 1. sec ²u-tan ²u/cos ²v+sin ²v ...
- Trigonometry - 1.Solve tan^2x + tan x – 1 = 0 for the principal value(s) to two ...

More Related Questions