If the function value y of positive proportion function y = (2a + 1) x decreases with the increase of X, then the value range of a is?

If the function value y of positive proportion function y = (2a + 1) x decreases with the increase of X, then the value range of a is?

The function value y of positive scale function y = (2a + 1) x decreases with the increase of X
Then k = 2A + 1