A+B=60degrees and CosA + Cos B=1 ....find
1) cos(A-B)
2)cosA - Cos B
You have: A+B=60° and cos(A)+cos(B)=1
If you write:
cos(A)+cos(B)=1 as 2cos((A+B)/2).cos((A-B)/2)=1
You can solve this one because you know A+B=60° so (A+B)/2=30°
You have now: 2cos(30°).cos((A-B)/2)=1
Now try to finish it.