math
posted by robert .
need an aswer quich ok thiers two the find sin(2pi/3 pi/4) using sum and difference identites and then tan 5pi/12 using the same identites

You have a formula for
Sin(AB)
Use that on the first one.
Now on the second, recall that
5PI/12= 3PI/12 + 2PI/12=PI/4 +PI/6
You now can use the tan (A+B) formula, as you know the tan(PI/4) and tan(PI/6)