How to create a mask for the area under a cosine curve?

HI all

I have created a cosine curve on my image (199 rows x 144 columns). I would like to only retain the values under the curve so that the values above the curve becomes NaNs. How do I do that? For example, how can I create a mask array to get 1s as elements below that curve and 0 or NaN above that curve?

This is my code I used for getting the curve:

t = 0:0.001:1000;
x = 90*cos(1/(23)*t)+110;
hold on;plot(t,x,'linewidth',2);
axis([1, 144, 1,199])

Any help is highly appreciated. Thank you!