Question

Mohon bantuannya yah !

Answer 1

Cari dulu turunannya :

yg a)

y = cos (x + π/6), brarti :

y' = -sin (x - π/6)

fungsi turun klo f'(x) < 0

-sin (x + π/6) < 0

sin (x + π/6) < 0

Jadi :

sin (x + π/6) = 0

sin (x + 30°) = sin 0°

x + 30° = 0° + k.360°

x = -30° + k.360°

k = 0, x = -30°

k = 1, x = 330°

k = 2, x = 690°

Atau :

x + 30° = (180°-0°)+k.360°

x + 30° = 180 + k.360°

x = 150° + k.360°

k = 0, x = 150°

k = 1, x = 510°

Jadi intervalnya :

0 < x+30° < 360°

0-30 < x+30-30< 360-30

-30° < x < 330°