"Proof of Euler's formula" The standard proof for Euler's formula, e^{i heta} = cos heta + i sin heta, uses the Taylor series of e^x, cos x, and sin x. This problem walks you through an alternate proof using ideas from differential equations. Let z = cos heta + i sin heta. Show that the differential of z is dz = (- sin heta + i cos heta)d heta. Show that dz = izd heta. Solve this first-order ODE by separating, using the initial condition z(0) = 1.