>>11260405It's ridiculous to memorize stuff like this. Allow me to assist you.
All you need is the pythagorean theorem, and SohCahToa.
The unit circle is a circle of radius 1, centered at the origin (as in pic related).
Any point on this circle can be used to form a right triangle as shown in blue, with the height of the triangle intersecting the X axis. This is known as a reference triangle.
Because the hypotenuse is 1, the base of the triangle on the unit circle is cosine, and the height is sine!
By the pythagorean theorem,
Substituting in the sides for our right triangle:
You can use this to derive the other identities for the most part.
As for the ridiculous quadrant chart, simply know that by drawing a right (reference) triangle for your point, you can trivially know the proper sign like this:
In quadrant two, sine is above the Y axis (so it's positive), and cosine is to the left of the X axis (so it's negative).
Tangent is sine over cosine, which is positive over negative, so it's negative.
The secant, cosecant and cotangent functions are just 1 over the other trig functions. 1 is a positive number, so it will always have the same sign.
There! Now you don't need to memorize any of that stupid chart!
