Question

what is the value of cos70°/cos110° ?

​

Answer 1

Step-by-step explanation:

In this task we have an expression like:

sin

x

sin

y

−

cos

x

cos

y

.

This can be rewritten as:

−

cos

x

cos

y

+

sin

x

sin

y

=

−

(

cos

x

cos

y

−

sin

x

sin

y

)

.

Expression in brackets is the right side of  

cos

(

x

+

y

)

identity, so our expression can be written as

−

cos

(

x

+

y

=

−

cos

(

110

+

70

)

=

−

cos

180

=

−

(

−

1

)

=

1