# Sin, Cos, Tan over 90°

#1
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°?
0
1 month ago
#2
you don't need to know any values over 90 i dont think
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#3
(Original post by jennaa21)
you don't need to know any values over 90 i dont think
Ah cool I was just revising on Seneca and it told me I needed to learn them; I was actually a bit confused because I'd never been told that before. Thanks
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1 month ago
#4
(Original post by bee-supernova)
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°?
You are supposed to know the shape of the sin cos and tan curves, where lines of symmetry are and how they repeat. Armed with this knowledge it's easy to work out trig values over 90.
While it's not strictly necessary, knowing sin 120 = sin 60 was potentially useful in the Edexcel non-calculator paper last week.
1
1 month ago
#5
For me, I love to use the geometric meaning of sin/cos to "remember" the values. i.e. drawing unit circles.

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.
Last edited by tonyiptony; 1 month ago
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