How can I solve this problem?Please,help.

Prove that,#(cos8theta+6cos6theta+13cos4theta+8cos2theta)/(cos7theta+5cos5theta+8cos3theta)=2costheta#

1 Answer
P dilip_k
Dec 20, 2017

#LHS#
#=(cos8theta+6cos6theta+13cos4theta+8cos2theta)/(cos7theta+5cos5theta+8cos3theta)#

#=(2costheta(cos8theta+6cos6theta+13cos4theta+8cos2theta))/(2costheta(cos7theta+5cos5theta+8cos3theta))#
#=(2costheta(cos8theta+6cos6theta+13cos4theta+8cos2theta))/(2costhetacos7theta+5*2costhetacos5theta+8*2costhetacos3theta)#

#=(2costheta(cos8theta+6cos6theta+13cos4theta+8cos2theta))/(cos8theta+cos6theta+5cos6theta+5cos4theta+8cos4theta+8cos2theta)#

#=(2costheta(cos8theta+6cos6theta+13cos4theta+8cos2theta))/(cos8theta+6cos6theta+13cos4theta+8cos2theta)#

#=2costheta=RHS#

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