Toán Rút gọn

lengoctutb

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28 Tháng hai 2016
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a)a) A=cos(π2+x)+cos(2πx)+cos(3π+x)=sinx+cos(x)+cos(π+x)=sinx+cosxcosx=sinxA=cos(\frac{\pi}{2}+x)+cos(2\pi -x)+cos(3\pi +x)=-sinx+cos(-x)+cos(\pi +x)=-sinx+cosx-cosx=-sinx

b)b) B=2cosx3cos(πx)+5sin(7π2x)+cot(3π2x)=2cosx3(cosx)+5sin(π2x)+cot(π2x)B=2cosx-3cos(\pi -x)+5sin(\frac{7\pi}{2} -x)+cot(\frac{3\pi}{2} -x)=2cosx-3(-cosx)+5sin(-\frac{\pi}{2} -x)+cot(-\frac{\pi}{2} -x)
B=2cosx+3cosx5sin(π2+x)cot(π2+x)=5cosx5cosx(tanx)=tanxB=2cosx+3cosx-5sin(\frac{\pi}{2}+x)-cot(\frac{\pi}{2}+x)=5cosx-5cosx-(-tanx)=tanx

c)c) C=2sin(π2+x)+sin(5πx)+sin(3π2+x)+cos(π2+x)=2cosx+sin(πx)+sin(π2+x)+(sinx)C=2sin(\frac{\pi}{2}+x)+sin(5\pi -x)+sin(\frac{3\pi}{2} +x)+cos(\frac{\pi}{2}+x)=2cosx+sin(\pi -x)+sin(-\frac{\pi}{2}+x)+(-sinx)
C=2cosx+sinxsin(π2x)sinx=2cosxcosx=cosxC=2cosx+sinx-sin(\frac{\pi}{2}-x)-sinx=2cosx-cosx=cosx

d)d) D=cos(5πx)sin(3π2+x)+tan(3π2x)+cot(3πx)=cos(πx)sin(π2+x)+tan(π2x)+cot(πx)D=cos(5\pi -x)-sin(\frac{3\pi}{2} +x)+tan(\frac{3\pi}{2} -x)+cot(3\pi -x)= cos(\pi -x)-sin(-\frac{\pi}{2}+x)+tan(-\frac{\pi}{2}-x)+cot(\pi -x)
D=cosx(sin(π2x))tan(π2+x)cotx=cosx+cosx(cotx)cotx=0D=-cosx-(-sin(\frac{\pi}{2}-x))-tan(\frac{\pi}{2}+x)-cotx=-cosx+cosx-(-cotx)-cotx=0
 
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