Find all solutions to the equation 5cosx415cosx41 in the int

Find all solutions to the equation 5cos(x+4)=15cos(x+4)=1 in the interval 0x20x2. If there is more than one answer, enter your answers as a comma separated list.

Solution

5cos(x+4)=15cos(x+4)=1

=>   5cos(x+4)=15cos(x+4) =>  5cos(x+4)=3 x (5cos(x+4)) ........(1)

=>   5cos(x+4)=1

=> using in(1)

1 = 3 x 1

=> 1 = 3

not possible. No solution exists