Do you know, what a recursive function is? You have to include a call to itself in the code. But this should not cause an infinite recursion, therefore you have to modify the inputs and outputs, such that the calling will end.
function Triangle(x)
disp(x)
if x > 0
Triangle(x - 1);
end
end
Now fill in your code to draw the stars.
By the way: repmat('*', 1, x) helps to create the string without a loop. See also:
sprintf('%20s', 'hello')
This fills in spaces on the left, such that the output has at least 20 characters.
