In a coordinate system, if the x component of a vector and the angle between the vector and x-axis are known, then the magnitude of the vector is calculated by which operation, taken with respect to the x component?
Can someone help me by explaining this i have an exam tomorrow so please hurry

Light from two different sources are incident upon the same side of a polarizing filter. light from one source is polarized with total intensity ip, while light from the other source is unpolarized with total intensity iu. as you rotate the polarizing filter through 360 degrees, the intensity of the transmitted light on the other side varies by a factor of 9. what is the relative intensity of the initial polarized source to the unpolarized source, or ip/iu?