tolong dong gimana caranya yang pinter jawab terimah kasih
Cos x + cos (x + 120)° + cos (x + 240)°
= cosx + (cosx.cos120 – sinx.sin120) + (cosx.cos240 – sinx.sin240)
= cosx + [cosx.cos(180-60) – sinx.sin(180-60)] + (cosx.cos(180+60) – sinx.sin(180+60)]
= cosx + (cosx.-0,5 – sinx.sin60) + (cosx.-0.5 – sinx.-sin60)
= cosx – 0,5cosx – sinx.sin60 – 0,5cosx + sinx.sin60
= (cosx – 0,5cosx – 0,5cosx) + (- sinx.sin60 + sinx.sin60)
= 0 + 0
= 0