How do you solve the equation on the interval [0,2pi) for #2sin (t) cos (t) + sin (t) -2 cos (t) -1 =0 #?

1 Answer
Jun 10, 2016

#pi/2, (2pi)/3, (4pi)/3#

Explanation:

Group the terms of the equation in order to factor it:
f(t) = (2sin t.cos t - 2cos t) + (sin t - 1 )= 0
f(t) = 2cos t(sin t - 1) + (sin t - 1) = 0
f(t) = (sin t - 1)(2cos t + 1) = 0
Solve the 2 binomials by using Trig Table and unit circle -->
a. sin t - 1 = 0 --> sin t = 1 --> # t = pi/2#
b. 2cos t + 1 = 0 --> #cos t = -1/2# --> # t = +- (2pi)/3#
Note that the arc #-(2pi)/3# is co-terminal to arc #(4pi)/3#
Answer for #(0, 2pi)#
#pi/2, (2pi)/3, (4pi)/3#