October 24th, 2017, 02:33 PM  #1 
Newbie Joined: Oct 2017 From: Brazil Posts: 3 Thanks: 0  Solve the inequation
Solve the inequation: cos*3 (a) . cos (3a)  sen*3 (a) . sen (3a) > 5/8

November 9th, 2017, 04:11 AM  #2 
Math Team Joined: Jan 2015 From: Alabama Posts: 3,261 Thanks: 894 
I recognize that "sen" would be, in English, "sin" but is "cos*3(a)" intended to be cos(a) to the third power (that I would write "cos^3(a)")? That is, is the inequality cos^3(a) cos(3a) sin^3(a)sin(3a)> 5/8? If so, I would be inclined to use the facts that cos(3a)= cos^3(a) 3cos(a)sin(a) and sin(3a)= sin(a)cos^2(a) sin^3(a). 

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inequation, solve, trigonometry 
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