Help with plotting sinusoidal wave

Hello, Im trying to plot a sinusoidal wave x(t) = 4cos(10*pi*t-pi/2) from -0.2 to 0.5 with 0.05 interval. The plot i get in matlab is a triangular wave and not a sinusoidal wave. am i missing any thing? :(

F = 5; A = 4; t = -0.2:0.05:0.5; phi = -pi/2; x = A*cos(2*pi*t*F + phi); plot(t,x) grid on

Answer 1

[Rick Rosson]

Compare your sampling rate (in samples per second) to the frequency of your sine wave (in hertz or cycles per second). What is the ratio (both numerical value and units of measure) of the sampling rate to the sine wave's frequency? What does this information imply about the sampled sine wave and the triangle wave that you are seeing?

To see what is happening a bit more clearly, try using the stem function instead of plot.

   stem(t,x);

HTH.