The negative slope of the production possibilities curve is a graphical way of indicating that:

Consider an economy where the government's budget is initially balanced. the production function, consumption function and investment function can be represented as follows y equals k to the power of alpha l to the power of 1 minus alpha end exponent c equals c subscript 0 plus b left parenthesis y minus t right parenthesis i equals i subscript 0 minus d r suppose that taxes increase. what happens to the equilibrium level of output?