Chapter 1, Problem 5P

Two waves, y₁(t) and y₂(t), have identical amplitudes and oscillate at the same frequency, but y₂(t) leads y₁(t) by a phase angle of 60°. If

     $y_1\left(t\right)=4\cos \left(2\pi \times {10}^{3}t\right),$

write the expression appropriate for y₂(t) and plot both functions over the time span from 0 to 2 ms.