The Student Room Group
Uni students - Complete our survey >>
Uni students - Complete our survey >>
Uni students - Complete our survey >>

C4 Trig Help

Express Cos(40)Cos(30) + Sin(40)Sin(30) in the form Sin(X)

I have tried putting into the form Cos(A+B) then using the cos+sin=1 identity to work it out but i get no where near the answer. I know it might seem an easy question but im not sure how to go about it.

Thanks for any help
Reply 1
Avatar for B_9710
B_9710
18
The expression is equal to cos(40-30)=cos(10)=sin(80)
Remember that cos(90-θ)=sinθ.
Reply 2
Avatar for TeeEm
TeeEm
19
Original post by ABC1123
Express Cos(40)Cos(30) + Sin(40)Sin(30) in the form Sin(X)

I have tried putting into the form Cos(A+B) then using the cos+sin=1 identity to work it out but i get no where near the answer. I know it might seem an easy question but im not sure how to go about it.

Thanks for any help


http://www.thestudentroom.co.uk/forumdisplay.php?f=38
Sin(a) = cos(90-a)
Cos(a) = sin(90-a)

(Im waiting for that cheeky rep)
Reply 4
Avatar for ABC1123
ABC1123
OP
1
Original post by B_9710
The expression is equal to cos(40-30)=cos(10)=sin(80)
Remember that cos(90-θ)=sinθ.


Thanks :smile:
Reply 5
Avatar for ABC1123
ABC1123
OP
1
Original post by GeologyMaths
Sin(a) = cos(90-a)
Cos(a) = sin(90-a)

(Im waiting for that cheeky rep)


Thanks, and you sure do get the rep!:smile:

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you