Solve the equatcn in the interval 0 2pi If there is more tha

Solve the equat.cn in the interval [0, 2pi]. If there is more than one solution write them separated by commas.

Solution

given cos²x - 1.3cosx - 0.48 = 0

let cosx = t then

t² - 1.3t - 0.48 =0

t = [1.3 + sqrt(1.69 + 1.92)] / 2 = [1.3 + 1.9] / 2

t = 1.015 , t= - 0.885

cosx = 1.015 ==> x = cos^-1(1.015) = it has no solution

cosx = -0.885 ==> x = cos^-1(-0.885) = 2.65729