It's impossible to be sure what you mean. Is it
?
Suppose E is a projection in M_2(C) with rank one. Show that there is a real number θ and a complex number β with |β| = 1 such that
E =
cos^2 βsinθcosθ
Bsinθcosθ sin^2 θ
M_2(C) represents an 2 x 2 matrix in the complex numbers.
Β represents β conjugate.