# How to complete this identity? (See picture). Thanks!

##### 2 Answers

Mar 11, 2018

Option B

#### Explanation:

Use the formula:

and then divide by the denominator,

you will get the answer.

Mar 11, 2018

Just to elaborate on the previous contributors answer, we have

#=(cosalphacosbeta + sinalphasinbeta)/(cosalphacosbeta)#

#= (cosalphacosbeta)/(cosalphacosbeta) + (sinalphasinbeta)/(cosalphacosbeta)#

#=1 + tanalphatanbeta#

Which is answer (b) as derived by the other contributor.

Hopefully this helps!