getting right t-value for sin wave

hey everyone, i have this problem that involves one part, i know how to do the problem just alittle confused about this part and hope you guys can help me out,

Generate a sine wave

y(t)=sin(2*pi*f*t+7*a)

and the problem asks to generate random value for a by using randn

this is what i got but cannot seem to get the right (t) to get the sin wave, how do i determine that?

t=??
f=10;
a=randn(1,length(t));
y=sin(2*pi*f*t+(7*a));
plot(t,y)thnx alot

[Andrew Newell]

What do you mean by "get the sin wave"?

[gedaa]

when i try different ranges for t, the wave doesn't look like a sin wave, it looks very distorted, like for example:

t=0:0.001:0.5;

[Walter Roberson]

The upper bound on your t should be an integer if you want a whole number of periods.

Answer 1

[Paulo Silva]

ok now I got it, if the objective is to add noise to a sine wave you are doing it the wrong way.

t=0:0.001:2
f=10;
a=randn(1,length(t));
y=a/10+sin(2*pi*f*t);
plot(t,y)

if the objective is to select a random phase than

t=0:0.001:2
f=10;
a=randn*2*pi; %something ?!
y=sin(2*pi*f*t+7*a);
plot(t,y)

[gedaa]

but you changed the equation they're asking for, they want this wave created:

y(t)=sin(2*pi*f*t+7*a)

[Paulo Silva]

7*a is where the phase is, is that what is asked for?

[gedaa]

i think the 2nd part you have makes sense, what i meant by 7*a is that it's part of the problem, i cannot take it out

[gedaa]

the objective to the problem is actually both, first find randn for a, and then generating noise and then adding it to the sin wav