Question

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

Answer 1

Option B

Explanation:

Use the formula:

`cos(a-b)=cosacosb+sinasinb`

and then divide by the denominator,
you will get the answer.

Answer 2

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!