熟悉三角函式公式
倒數關係: tan cot=1 sin csc=1 cos sec=1 商的關係： sin/cos=tan=sec/csc cos/sin=cot=csc/sec 平方關係： sin^2()+cos^2()=1 1+tan^2()=sec^2() 1+cot^2()=csc^2()
正弦 sin2A=2sinAcosA 餘弦 2a=Cos^2(a)-Sin^2(a) =2Cos^2(a)-1 =1-2Sin^2(a) 2a=1-2Sin^2(a) 2a=2Cos^2(a)-1 正切 tan2A=(2tanA)/(1-tan^2(A))
cos(+)=coscos-sinsincos(-)=coscos+sinsinsin(+)=sincos+cossinsin(-)=sincos -cossin
積化和差
sinsin = [cos(-)-cos(+)] /2 coscos = [cos(+)+cos(-)]/2 sincos = [sin(+)+sin(-)]/2 cossin = [sin(+)-sin(-)]/2
誘導公式
sin(-) = -sin cos(-) = cos tan (-)=-tan sin(/2-) = cos cos(/2-) = sin sin(/2+) = cos cos(/2+) = -sin sin() = sin cos() = -cos sin() = -sin cos() = -cos tanA= sinA/cosA tan(/2+)=-cot tan(/2-)=cot tan()=-tan tan()=tan 誘導公式記背訣竅：奇變偶不變，符號看象限
萬能公式
sin=2tan(/2)/[1+(tan(/2))2] cos=[1-(tan(/2))2]/[1+(tan(/2))2] tan=2tan(/2)/[1-(tan(/2))2]
