Homework Help: Trig Equation

Posted by sqleung on Saturday, March 1, 2008 at 1:52am.

Solve for x (exact solutions):

sin x - sin 3x + sin 5x = 0

-Іа Ём x Ём 0

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Now, using my graphics calculator, I discovered that the following equation has 5 solutions. I have managed to come up with 3 of them but I'm having trouble finding the other 2. My 3 answers are:

0, -Іа/6, -5Іа/6

I need the answers to be EXACT like above so any help would be appreciated. Thankyou.

Trig Equation - drwls, Saturday, March 1, 2008 at 7:25am
I answered this question two days ago. Once of the answers is of course x = 0. For the others, I substitued indentities for sin 3x and sin 5x in terms of sin x, and ended up with a factorable equation for sin x. This leads to exact equations for arcsin in terms of fractions.

I am not able to read your terms -Іа/6 and -5Іа/6

If I can find my original answer, I will post a link to it below
- Trig Equation - drwls, Saturday, March 1, 2008 at 7:46am
  OK, I found my original answer at
  http://www.jiskha.com/display.cgi?id=1204243109
  and it has two mistakes, a missing exponent and an incorrect sign. I should have ended up with the equation
  3sinx - 16 sin^3x + 16sin^5x = 0
  which factors to
  sinx (3 - 16sin^2x + 16sin^4x) = 0
  sinx (4sin^2x-3)(4sin^2x -1) = 0
  Thge roots, besides x=0, are:
  sin^2x = 1/4
  sin x = +/-sqrt(1/2)
  and
  sin^2 = (3/4)
  sin x = +/-(sqrt3)/2
Trig Equation - drwls, Saturday, March 1, 2008 at 10:31am
Any positive or negative integral multiple of 30 degrees (x=pi/6), including 0 degrees, satisfies the equation.
- Trig Equation (correction) - drwls, Saturday, March 1, 2008 at 11:25am
  All +/- integral multiples of pi/6 EXCEPT multiples of pi/2 are solutions

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