Posted by **Jerry** on Tuesday, November 13, 2012 at 9:47am.

cos(X+pi/6) + sin(x-pi/3) = 0

I am working with one side but I am not sure if I can subtract at all here.

- Prove or disprove? -
**Reiny**, Tuesday, November 13, 2012 at 10:08am
To see if it is an identity, pick any value of x

e.g. x = 78°

then x+π/6 ---> 78+30 = 108°

and x-π/3 ---> 78 - 60 = 18°

is cos108 + sin18 = 0 ???

YES

ok, then , let's prove it

LS = cosxcosπ/6 - sinxsinπ/6 + sinxcosπ/3 - cosxsinπ/3

= √3/2 cosx -1/2 sinx + 1/2 sinx - √3/2 cosx

= 0

= RS

- Prove or disprove? -
**Steve**, Tuesday, November 13, 2012 at 10:23am
or, since we know that cos(pi/2 - x) = sin(x)

cos(pi/2 - (x+pi/6)) = sin(pi/3 - x) = -sin(x-pi/3)

## Answer This Question

## Related Questions

- Prove or Disprove - Cos(X+y)cos(x-y)= cos^2theta - sin^2theta I foiled the left ...
- trig - it says to verify the following identity, working only on one side: cotx+...
- TRIG! - Posted by hayden on Monday, February 23, 2009 at 4:05pm. sin^6 x + cos^6...
- Precalculus with Trigonometry - Prove or disprove the following Identities: cos...
- MATH - Hi, I really need help with these questions. I did some of them halfway, ...
- Mathematics - Trigonometric Identities - Let y represent theta Prove: 1 + 1/tan^...
- Trigonometry desperate help, clueless girl here - 2. solve cos 2x-3sin x cos 2x...
- Precalc - Prove or disprove the following identity. cos(-x) - sin(-x) = cos(x...
- Precalculus with Trigonometry - Prove or disprove the following identity: (sin(...
- math - Prove that for all real values of a, b, t (theta): (a * cos t + b * sin t...

More Related Questions