Cosine (cos) is equal to the ratio of adjacent side to hypotenuse; cosA=b/c

Tangent (tan) is equal to the opposite side of the adjacent side; tanA=a/b

Knowledge point 2 1. Square relation: sin? a+cos？ A= 12。 Business relationship: tana=sina/cosa.

Knowledge three sin (90-α) = cos α, cos (90-α) = sin α, tan (90-α) = cot α, and cot (90-α) = tan α.

Knowledge point 41/2; √2/2; √3/2;

√3/2; √2/2; 1/2;

√3/3; 1; √3