MATLAB: Plot a sine wave with the following… how to plot it

sine wave

Create a time vector, sine wave, 5 periods, 1 kHz, amplitude 2 volts in 5 x 1024 samples (time axis) as well as 5 periods in 4096 samples

You're very close:

freq=1000;%1 kHz
t=linspace(0,5,1024)/freq;%from 0 to 5 periods in 1024 steps
A=2;%amplitude
x=A*sin(freq*t*2*pi);
plot(t,x)

I don't really see how more samples will change things, but you can just change the linspace parameters.

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Francis - from an example at fft, we can do

 t = 0:0.01:1;
 f = 15;
 a = 4;
 y = a*sin(2*pi*f*t);
 plot(t,y);

Though ten samples (your t) may not be enough to accurately represent the sine wave (that you are attempting), so try

 Fs = 1000; 
 t = linspace(0,1-1/Fs,Fs);
 f = 15;
 a = 4;
 y = a*sin(2*pi*f*t);
 plot(t,y);

T = 6; 
Fs = 1e3;
dt = 1/Fs;
t = 0:dt:T-dt;
a = 4;
x = a*sawtooth(2*pi*t);
t = t*5; 
plot(t,x) 
grid on