Trigonometry

Sum and difference of trigonometric functions

Keywords: sum and difference of trigonometric functions

s i n α + s i n β = 2 s i n α + β 2 · c o s α β 2
s i n α s i n β = 2 c o s α + β 2 · s i n α β 2
c o s α + c o s β = 2 c o s α + β 2 · c o s α β 2
c o s α c o s β = 2 s i n α + β 2 · s i n α β 2
t g α ± t g β = s i n ( α ± β ) c o s α · c o s β
c t g α + c t g β = s i n ( α + β ) s i n α · s i n β
c t g α c t g β = s i n ( β α ) s i n α · s i n β