再过两个月就要大考了。我还是抓不到这棵的诀窍。
谁可以告诉我遇到些问题是该用什么样的解答方法。
例：Prove each of the following trigonometric functions
(a) (sin x + cos x)^2 = 1 = sin 2x
(b) cos^4 y - sin^4 y = cos 2y
(c) sin (A-B) / cosA cosB = tanA- tanB
(sin x + cos x)^2 = 1 +sin 2x Proof: for (sin x + cos x)^2=sinx^2+cosx^2+2sinxcosx=1+sin2x cos^4 y - sin^4 y = cos 2y Proof: for cosy^2^2-siny^2^2=(cosy^2+siny^2)(cosy^2-siny^2)=cosy^2-siny^2=cos 2y sin (A-B) / cosA cosB = tanA- tanB Proof: for sin(A-B)=sinAcosB-sinBcosA so sin (A-B) / cosA cosB =sinAcosB-s
