Posted by Jack on October 21, 2002 at 08:10:45:
In Reply to: pre-calc confusion help plz!!!!! posted by Jacquie on October 20, 2002 at 19:09:01:
: ok im totally lost on how to do the following problems. ive tried to do each one but keep getting answers that are no where near what they should be. (plz include all steps if u know how to do it tnx)
: 1. prove the identity
: tan(3pie/4 - z)= (tan z + 1)/(tan z - 1)
: Did not have time to work this one. Usually a good place to start is to first convert to sin and cos. For example, tan(3pi/4 - z)=sin(3pi/4 - z)/cos(3pi/4 - z). Then use the sin and cos addition identities.
: 2. prove the identity
: sin(x+y) + sin (x-y)= 2sinxcosy
: Use the ADDITION IDENTITIES
: sin(a+b)=sinacosb+cosasinb and sin(a-b)=sinacosb-cosasinb
: Make the subs and combine terms
: 3. find the value
: cos(3pie/8)
: 3pi/8 ~ 67.5 degrees
: cos(67.5) = .383