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October 24th, 2017, 03:33 PM   #1
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Solve the inequation

Solve the inequation: cos*3 (a) . cos (3a) - sen*3 (a) . sen (3a) > 5/8
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November 9th, 2017, 05:11 AM   #2
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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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