Need assistance with C3 trigonometry proof question

Hi!

Please could you help me with answering the following proof question for trigonometry in C3. 

23) Prove that if P, Q and R are the angles of a triangle, then

Thanks!

Student X

P+Q+R=180 deg 

P+Q = 180 deg -R 

tan(P+Q) = tan (180 deg -R) 

(tanP +tanQ)/ (1- tanP tanQ) =-tanR 

(Note: tan 180 deg =0 ) 

Proceed with a little more housekeeping of the above, and you should arrive at the required proof shortly. 

Hope this helps. Peace.

Best Regards,

Mr Koh