Sin, Cos, Tan over 90°Watch this thread
Hey; I'm revising for a maths end of year and apparently you have to know the sin, cos and tan of certain angles off by heart- I can remember the ones we need to know under 90 but is there a way to remember sin cos and tan for 120, 135, 150 and 180°?
While it's not strictly necessary, knowing sin 120 = sin 60 was potentially useful in the Edexcel non-calculator paper last week.
Just a quick revision, we define, geometrically, the coordinates of any point on the unit circle be .
Then, if you know the sines and cosines of 30, 45 and 60 degrees, and you know how to find coordinates of a point when it's reflected along an axis or rotated about the origin, you can get to what you want.
For instance, sine 120 degrees is asking the question "what's the y-coordinate of the point on the unit circle with angle 120 degrees" (Note: if someone could help me word this better, it'd be great), which happens to be the same as that of angle 60 degrees, as it's just a reflection of the point along the y-axis.
I encourage you to doodle a bit to see what I mean.
EDIT: tan is just sin/cos, though it does have a cool geometric meaning as well.