cosa=±1−sin2a,tana=sina/cosa
Precalculate:
cosx=1−(4/5)2=3/5,tanx=4/3
cosy=1−(−12/13)2=5/13,tany=−12/5
Answer:
a)cos(x+y)=cosx⋅cosy−sinx⋅siny=3/5⋅5/13−4/5⋅(−12/13)=63/65
b)tan(x−y)=(tanx−tany)/(1+tanx⋅tany)=(4/3−(−12/5))/(1+4/3⋅(−12/5))=56/(15−48)=−56/33
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