posted by Patrick on .
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.
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?