Question

cos(x) + cos(x-pi) + cos (x +pi) =?​

Answer 1

Step-by-step explanation:

Explanation:

We use the Formula

:

cos

(

A

+

B

)

=

cos

A

cos

B

−

sin

A

sin

B

Letting,

A

=

,

&

,

B

=

π

, we get,

cos

(

x

+

π

)

=

cos

x

cos

π

−

sin

x

sin

π

Since,

cos

π

=

−

1

,

and

,

sin

π

=

0

,

cos

(

x

+

π

)

=

−

cos

x

.