Question 1174716
here's a reference in trig identities you might find useful.


<a href = "https://www.purplemath.com/modules/idents.htm" target = "_blank">https://www.purplemath.com/modules/idents.htm</a>


the derivation is from tan(x + y) = sin(x + y) / cos(x + y) which i believe is because tangent = sine / cosine.


here's a proof on why tan(x + y) = sin(x + y) / cos(x + y)


<a href = "https://socratic.org/questions/how-do-you-solve-tan-x-y-tan-x-tan-y-1-tan-x-tan-y#138400" target = "_blank">https://socratic.org/questions/how-do-you-solve-tan-x-y-tan-x-tan-y-1-tan-x-tan-y#138400</a>