Posted by **Patrick** on Wednesday, April 22, 2009 at 10:54am.

Use the sum or difference identity to find the exact value of sin255 degrees.

My answer: (-sqrt(2)- sqrt(6)) / (4)

Find the value of tan (alpha-beta), if cos alpha= -3/5, sin beta= 5/13, 90<alpha<180, and 90<beta<180.

My answer: -33/56

Which expression is equivalent to cos(pi-theta)?

Is it -cos theta?

Which expression is not equivalent to cos 2theta?

a. cos^2 theta- sin^2 theta

b. 2cos^2 theta - 1

c. 1 - 2sin^2 theta

d. 2sin theta cos theta

I would pick D.

- Pre Calc. -
**Reiny**, Wednesday, April 22, 2009 at 11:23am
correct on all counts, good job

For questions on finding "exact" values for certain trig ratios, a quick way to check your result is to simply evaluate your answer with a calculator, then compare it to the calculator result for the initial trig ratio

e.g. for yours I found (-sqrt(2)- sqrt(6)) / (4) to be -.9659258

and sin 255 to be -.9659258 , not bad eh?

## Answer This Question

## Related Questions

- trig - evaluate the following in exact form, where the angeles alpha and beta ...
- Math - Given that sin alpha=4/sqrt65, pi/2<alpha<pi, and cos beta=-3/...
- Math/Calculus - Solve the initial-value problem. Am I using the wrong value for ...
- Math ( Polynomial ) - This time three questions - 1. If (x^2 - 1 ) is a factor ...
- Math ( Polynomial ) - This time three questions - 1. If (x^2 - 1 ) is a factor ...
- Calculus - The question will first read in English followed by a reading in ...
- Math - If alpha and beta are the zeros of the polynomial ax^2 + bx + c then ...
- Trig. - I have answers for these problems, but I wanted to check if I had them ...
- physics - Two radar stations A and B, are separated by horizontal distance of (...
- maths - if alpha and beta are the zeros of the polynomial 2x^2-4x+5 then find ...

More Related Questions