Question

Solve 2cos(x)-4sin(x)=3 [0,360]

Answer 1

2cos(x) - 4sin(x) = 3

use identity  [cos(x)]^2 +[ sin(x)]^2 = 1 => cos(x) = √[1 - (sin(x))^2]

2√[1 - (sin(x))^2] - 4 sin(x) = 3

2√[1 - (sin(x))^2] = 3 + 4 sin(x)

square both sides

4[1 - (sin(x))^2] = 9 + 24 sin(x) + 16 (sin(x))^2

expand, reagrup and add like terms

4 - 4[sin(x)]^2 = 9 + 24sin(x) + 16sin^2(x)

20[sin(x)]^2 + 24sin(x) +5 = 0

use quadratic formula and you get sin(x) = -0.93166 and sin(x) = -0.26834

Now use the inverse functions to find x:

arcsin(-0.93166) = 76.33 degrees

arcsin(-0.26834) = 17.30 degrees