Question

find cos120° and sin120°​

Answer 1

Step-by-step explanation:

cos120° = cos(90+ 30)°

{cos(A+B)= cosAcosB - sinAsinB}

cos(90+30)°= cos90*cos30 - sin90*sin 30

= 0×√3/2 - 1 × 1/2

=-1/2

sin120° = sin(90°+ 30°)

{sin(A+B) = sinAcosB + cosAsinB}

sin(90+30)° = sin90*cos30 + cos90*sin30

= 1 × √3/2 + 0 × 1/2

= √3/2

Answer 2

sin120 can be written as sin(90+30)  

and sin (90+x)= cosx  

then sin(90+30) =cos30 =√3/2

similarly cos 120= cos(90+30) =-sin 30 =-1/2    [cos(90+x) =-sinx]

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