How do you answer y=sin(x) for angle -90, -60, and -45 degrees?

Question

debbieg · Answer

I guess you mean:

sin(-90)= ?
sin(-60)= ?
sin(-45)= ?

It kind of depends on what methods you have covered. If your teacher is stressing the unit circle, then those are on there, so you would look at the y-coordinate of each point of intersection with the circle.

Alternatively, for -90 you have a quadrantal angle. since $\sin\alpha=y/r$ then you have to notice that, for any point on the negative side of the y-axis, y/r=-1.

For the other two, those are not quadrantal so I would use their reference angles to find the function values. Sine is negative in Q4, so you have:

sin(-60)=-sin(60)
And 
sin(-45)=-sin(45)

For sin(60) and sin(45) then, you could use SOHCAHTOA with the appropriate "special triangle":
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