Trigonometry
Is the given equation an identity?
sin(x−y)cos(x+y)=tanx−tany1−tanxtany\frac{\sin\left(x-y\right)}{\cos\left(x+y\right)}=\frac{\tan x-\tan y}{1-\tan x\tan y}cos(x+y)sin(x−y)=1−tanxtanytanx−tany
Yes
No