How would i write this expression as the sine , cos, or tangent of a single angle?

cos(π/5)cos(π/7)+sin(π/5)sin(π/7)

Question

How would i write this expression as the sine , cos, or tangent of a single angle? 

cos(π/5)cos(π/7)+sin(π/5)sin(π/7)

anonymous · Answer

$$\cos(A-B)$$
Do you know the expansion of this?

anonymous · Answer

So it would be...
Cos(π/5-π/7)?

anonymous · Answer

@koushik_ksv ?

anonymous · Answer

Yeah, even the other way round $$\cos (\Pi/7 - \Pi/5)$$. Its the same..

anonymous · Answer

ok so my final answer would be cos (pi/2)? Im not sure how to subtract radians

anonymous · Answer

what is $\frac{1}{5}-\frac{1}{7}$ ?

anonymous · Answer

don't let the arithmetic fool you
ignore the $\pi$ and just subtract

anonymous · Answer

2/35.

anonymous · Answer

Oh so 2pi/35?

anonymous · Answer

yes

anonymous · Answer

So the final answer would be cos (2pi/5)...correct?

anonymous · Answer

if you meant "cos (2pi/35)" then yes

anonymous · Answer

oh yes right. But since the question asks of a single angle should i convert to degrees?

anonymous · Answer

@satellite73 , could you please help me really quick.

anonymous · Answer

forget degrees, they have nothing to do with this problem

anonymous · Answer

Ok thanks @satellite73

anonymous · Answer

$\frac{2\pi}{35}$ is a number, but also a measure of an angle in radian