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# Write each of the following as a trigonometric ratio of an acute angle watch

1. Cos237
Sin312

can anyone help me answer these questions?
do i have to use a CAST diagram?
2. (Original post by rameow)
Cos237
Sin312

can anyone help me answer these questions?
do i have to use a CAST diagram?
You can use a cast diagram...

Could do it by inspection of the graphs as wel.
3. Yeah, although I always find it easier to just think about the graph.

You know sin(x) = sin(180-x) = -sin(-x) = -sin(180+x) = -sin(360-x) so just pick whichever one of these gives you an acute angle for the term in the brackets etc

cos(x) has similar (but not the same) identities. Finally you also know that cos(x) = sin(x+90)
4. (Original post by SeanFM)
You can use a cast diagram...

Could do it by inspection of the graphs as wel.
How could i use it?
5. (Original post by Darth_Narwhale)
Yeah, although I always find it easier to just think about the graph.

You know sin(x) = sin(180-x) = -sin(-x) = -sin(180+x) = -sin(360-x) so just pick whichever one of these gives you an acute angle for the term in the brackets etc

cos(x) has similar (but not the same) identities. Finally you also know that cos(x) = sin(x+90)

Im really sorry but how would i know that it gives me an acute angle?
6. (Original post by rameow)
How could i use it?
It's very much like having a value between 0 and 180 and then finding all the other values... instead you have a value between 180 and 360 and finding all the other values
7. so for sin(312), you'd want to pick the identity sin(x) = -sin(360-x) because 360-312 is 48 which is an acute angle. So you answer would be sin(312) = -sin(48)

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