If we took E with angle theta given with X axis
then in this case vector has an adjacent component along x direction
now using geometry we can say
[tex]cos\theta = \frac{adjacent}{hypotenuse}[/tex]
now we need to find its adjacent component along x axis
so we can write it as
[tex]E_x = E cos\theta[/tex]
now similarly in other way if we took angle phi
then we can say by geometry
[tex]sin\phi = \frac{opposite}{hypotenuse}[/tex]
now we need to find the opposite component of vector E
so here it is
[tex]x = E sin\phi[/tex]
