In a right triangle

Sin is the hypotenuse of the opposite side.

Cos is adjacent to the hypotenuse.

Tan is the villain.

In RT triangle ABC, sinA=a/c, cosA=b/c, tanA=a/b, and so on, 1. Inductive formula: sin (-a) =-sin (a) cos (-a) = cos (π 2-a) = cos (a) cos (π 2-a) = sin (a) sin (π 2+a) = cos (a). =-sin(a)cos(π+a)=-cos(a)2。 The trigonometric function sin (a+b) = sin (a) cos (b)+cos (α) sin (b) cos (a+b) = cos (a) cos (b). = Cos(a)Cos(b)+sin(a)sin(b)tan(a+b)= tan(a)+tan(b) 1-tan(a)tan(b)= tan(a)-tan(b)Cos(a-B2)sin(a)sin(b)= 2cos(a+B2)sin(a+B2)Cos(a)+Cos(b) = 2cos(a+B2)Cos(a-B2)Cos(a)-Cos(b)=-2s= cos 2(a)-sin 2(a)= 2 cos 2(a)- 1 = 1-2 sin 2(a)5。 Half-angle formula sin2 (A2) =1-cos (a) 2cos2 (A2) = 65438. =sina 1+cos(a)6。 The general formula sin (a) = 2tan (a2)1+tan2 (a2) cos (a) =1-tan2 (a2)1+tan2 (a2)+bcos (a) = a2+b2sin (a+c). = a2+b2cos(a-c) where tan (c) = ab1+sin (a) = (sin (a2)+2 formula classification formula expression multiplication and factorization a2-B2 = (a+b) (a-b) a3+B3 = (a+b) (a2 -b ≤ a ≤ b | a-b |≥| a |-b |-a |≤ a | the solution of a quadratic equation-b+√ (B2-4ac)/2a-b-b+√ (B2-4ac)/2a root and the coefficient x65438+. 0 Note: The equation has a real root B2-4ac.

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