Posted by Waldo on Monday, March 14, 2011 at 6:30pm.
Find all values of theta in the interval 0 <= theta < 360 that satisfy the equation 3cos(2theta)=7cos(theta). Express answers to the nearest ten minutes.
- Trig - bobpursley, Monday, March 14, 2011 at 6:39pm
u= 1/3 u= -2/3
so what angles are those?
- Trig - Reiny, Monday, March 14, 2011 at 6:39pm
3(2cos^2 Ų - 1) = 7cosŲ
6cos^ Ų - 7cosŲ - 3 = 0
(3cosŲ+1)(2cosŲ-3) = 0
cosŲ = -1/3 or cosŲ = 3/2, the last is not possible
cosŲ = -1/3
Ų must be in II or III
Ų = 180 - 70.529 or Ų = 180 + 70.529
= 109.471° or 250.053°
I assume you know how to change those decimals to degrees and minutes.
- Trig - Reiny, Monday, March 14, 2011 at 6:48pm
I must respectfully disagree with bob
cos 2T = cos^2 T - sin^2 T = 2cos^2 T - 1
bob had it backwards, time for a strong coffee.
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