The following question is from : COMMUNICATIONS SYSTEM ENGINEERING. 2
EDITION BY JOHN G.PROAKIS, MASOUD SALEHI.

CHAPTER 3, QUESTION 3.7 

an AM SIGNAL HAS THE FORM :
u(t)=[20+2cos3000pit+10cos6000pit]cos2pifct,,fc=100000hz,
1. Sketch the (voltage) spectrum of u(t)
2. Determine the power in each of the frequency components
3. Determine modulation index
4. Determine the power in sidebands,total power,ratio of sideband
power to total power

1. if you want to draw u(t) just use matlab. But if you want Frequency
domain spectrum use fourier transform properties. for a signal of type
v(t)*cos(2pifct) is 0.5*(v(f-fc)+v(f+fc)). just use the same rule for
all the other terms except for 20*cos2pifct for which it is a
deltafunction shifted by fc.
delta(f-fc)+delta(f+fc).

2. to find the power Integrate the above found frequency spectrum from
-infy to +infy.

3. try to write u(t) into something like a(1+m.k(t))cos2pifct. where m
is your modulation index. just use the property cos(a+b) =
cosacosb-sinasinb & cos(a-b) = cosacob+sinasinb.

4. same as 2.

1.)I wanted to know whether the voltage and frequency spectrum are the same?
2.)How do I do this in matlab?

1. Volatage spectrum is a spectrum of the function ut in matlab. 
If you want the answer ,

t = 0.0:0.00001:0.01;
ut = 20*cos(2*pi*100000*t)+cos((3000*pi+2*pi*100000)*t)+cos((3000*pi-2*pi*100000)*t)+5*cos((6000*pi+2*pi*100000)*t)+5*cos((6000*pi-2*pi*100000)*t);
plot(t,ut);
title('u(t) as a function of time');
xlabel('time');
ylable('u(t)');
ylabel'u(t)');
ylabel('u(t)');

Is modulation index =1/10

Thanks for the update!Can you show me how to do find modulation index
and power in the sidebands?
Thankyou