heeeeelp me

sinx = cos(90 - x) 

tanx = cot(90 - x) 

csc x = sec(90 - x) 

Using these, 
sin60 = cos(90 – 60) = cos 30 

sin45 = cos(90 – 45) = cos 45 

cos x = sin (90- x) 

cot A = tan(90 – A) 

csc30 = sec(90 – 30) = sec 60 

sec B = csc(90 – B) 

Write trigonometric function in terms of its cofunction 
sin(x + y) = cos (90 - (x + y)) 

= cos(90 - x - y) 

sin(60 - x) = cos (90 - (60 - x)) 

= cos(90 - 60 + x) 

= cos (30 + x) 

cos(20 + A) = sin (90 - (20 + A)) 

= sin ( 90 - 20 - A) 

= sin (70 - A) 

cos(A + B) = sin (90 - (A + B)) 

= sin (90 - A - B) 

cot(45 - x) = tan (90 - (45 - x))  

= tan (90 - 45 + x) 

= tan (45 + x) 


sec(30 - θ) = csc (90 - (30 - θ)) 

= csc (90 - 30 + θ) 

= csc (60 + θ) 

 

Thanks Ninjahamster, you have put in a lot of work there.

Welcome to the forum too.

I woud just have said

sin(x+y) = cos(90-x-y)

But your answer is much more comprehensive :)