about the unit circle
The unit circle is a circle with a radius of one. The center of the circle is the origin point (0,0). The unit circle can help measure sine, cosine, and tangent, and their inverses. The circle is made of four quadrants, quadrants I, II, III, and IV. In quadrant I, both cosine and sine are positive; quadrant II cosine is negative, and sine is positive; quadrant III both cosine and sine are negative; quadrant IV cosine is positive and sine is negative.