Since you depend on your previous answers, you can simply loop through the equations and store the answers.
x = ones(1,10); % also contains your initial x
y = ones(1,10); % just to preallocate y as well
for i=1:9 % loop 9 times
y(i) = 2*x(i) + 5; % calculate the y-value
x(i+1) = 2*y(i) + 5; % calculate the 'next' x-value
end
y(10) = 2*x(10) + 5; % finish off by calculating the final y-value
If you only care about the final value, this suffices:
x = 1;
for i=1:9
y = 2*x + 5; % calculate the y-value
x = 2*y + 5; % calculate the 'next' x-value
end
y = 2*x + 5;
