Question

Solve the equation: cos5x=cos7x , for x E [0,PI]

Answer 1

if cos a = cos b, then a=b or a=-b

here cos5x=cos7x, then 5x=7x or 5x=-7x

so what's the solution for these equations ?

Answer 2

7X=+-5X+2K(PI) ,K E Z;

Answer 3

2K(PI) represent k complete turns of a circle,
and since you want the answer in E [0,PI] , the 2K(PI) is canceled

Answer 4

sorry i wrote the general form , not particularized for this problem

Answer 5

but now i've got the solutions x={kpi/6/where k={0,1,2,3,4,5,6};}

Answer 6

@ifrimpanainte your answer is right! i had a mistake, sorry.
you need an explanation for that? or you got it ?

Answer 7

no thanks i've got it