Question

sin5π/18+cos4π/9=cosπ/9
​

Answer 1

Step-by-step explanation:

you must know the Cd formulae

cos c + cosD=2 cos (C+D)/2. cos(C-D)/2

LEFT. HAND SIDE

split the

1. 5pie/18
2. pie/2-4pie/9
3. you will get
4. both term in cos and
5. then use C+D formulae
6. ok