Question

cos 510x cos 330 +sin 390× cos 120

Answer 1

Hi ,

1 ) cos 510 = cos ( 360 + 150 )

= Cos 150

= Cos ( 180 - 30 )

= - cos 30°

2 ) cos 330° = cos ( 360 - 30 )

= Cos 30

3 ) sin 390 = sin( 360 + 30 )

= Sin 30

4 ) cos 120 = cos ( 90 + 30 )

= - sin 30°

Now ,

Cos 510 cos 330 + sin390 cos 120

= ( -cos 30°)(cos 30°)+(sin30°)(-sin30°)

= - cos² 30° - sin² 30°

= - ( cos² 30° + sin² 30° )

= -1

I hope this helps you.

: )

Answer 2

This is easy!!

1 ) cos 510 = cos ( 360 + 150 )

= Cos 150

= Cos ( 180 - 30 )

= - cos 30°

Using the formula cos 180-¤=-cos¤

2 ) cos 330° = cos ( 360 - 30 )

= Cos 30

3 ) sin 390 = sin( 360 + 30 )

= Sin 30

4 ) cos 120 = cos ( 90 + 30 )

= - sin 30°

Now ,

Cos 510 cos 330 + sin390 cos 120

= ( -cos 30°)(cos 30°)+(sin30°)(-sin30°)

= - cos² 30° - sin² 30°

= - ( cos² 30° + sin² 30° )

= -1

Please mark as the brainliest

Thanks!