Question

Jika cos x = cos 5phi/2 cos phi/12 + sin 5phi/2 sin phi/12, maka nilai x adalah....
a.3/5 phi
b.2/3 phi
c. 1/3 phi
d. 1/5 phi
e. 1/6 phi
dimohon dengan penjelasannya. trms

Answer 1

Cos x = cos(5π/2) cos(π/12) + sin(5π/2) sin(π/12)

ingat!!!

cos(a - b) = cos a cos b + sin a sin b

sehingga bentuk
cos(5π/2) cos(π/12) + sin(5π/2) sin(π/12)
menjadi
cos(5π/2 - π/12)
cos(29π/12)
x = 29π/12

mungkin salah soal

kalo soalnya gini
cos x = cos(5π/12) cos(π/12) + sin(5π/12) sin(π/12)

jadi cos(5π/12 - π/12)
= cos(4π/12)
= cos(π/3)

x = 1/3π