$(2$ pts$)$ For each of the sinusoidal source functions shown, determine the complex exponential source $($or just complex source as mentioned in the notes$)$ that has the given source as its real part. $($Hint: remember the real part must be a cosine$)$

a$)v(t)=5cos(6t)$

b$)v(t)=5sin(6t)$

c$)v(t)=10sin(2t-120)$

d$)v(t)=3cos(10t+135)$