Differentiation of Trigonometric Functions
📂FunctionsDifferentiation of Trigonometric Functions
The derivatives of trigonometric functions are as follows.
dxdsinxdxdcosxdxdtanx=cosx=−sinx=sec2xdxdcscxdxdsecxdxdcotx=−cscxcotx=secxtanx=−csc2x
Proof
Sum formulas for trigonometric functions
sin(α±β)=sinαcosβ±cosαsinβcos(α∓β)=cosαcosβ±sinαsinβ
Limit of the sine function
x→0limxsinx=1
Limit of the cosine function
x→0limx1−cosx=0
(sinx)′=cosx
By the definition of derivatives,
h→0limhsin(x+h)−sinx=h→0limhsinxcosh+sinhcosx−sinx=sinxh→0limhcosh−1+cosxh→0limhsinh=sinx⋅0+cosx⋅1=cosx(∵삼각함수의 덧셈공식)
■
(cosx)′=−sinx
By the definition,
h→0limhcos(x+h)−cosx=h→0limhcosxcosh−sinhsinx−cosx=cosxh→0limhcosh−1−sinxh→0limhsinh=cosx⋅0−sinx⋅1=−sinx(∵삼각함수의 덧셈공식)
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(tanx)′=sec2x
Quotient rule
(gf)′(x)=g2(x)f′(x)g(x)−f(x)g′(x)
By the quotient rule,
tan′x=(cosxsinx)′=cos2xsin′xcosx−sinxcos′x=cos2xcosxcosx+sinxsinx=cos2x1=(cosx1)2=sec2x
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(cscx)′=−cscxcotx
By the chain rule,
dxdcscx=dxd(sinx1)=d(sinx)d(sinx1)dxd(sinx)=−sin2x1cosx=−sinx1sinxcosx=−cscxcotx
■
(secx)′=secxtanx
By the chain rule,
dxdsecx=dxd(cosx1)=d(cosx)d(cosx1)dxd(cosx)=−cos2x1(−sinx)=cosx1cosxsinx=secxtanx
■
(cotx)′=−csc2x
(cotx)′=(sinxcosx)′=sin2x(cosx)′sinx−cosx(sinx)′=sin2x−sin2x−cos2x=−sin2x1=−csc2x