Homothetic functions are functions whose marginal technical rate of substitution (the slope of the isoquant, a curve drawn through the set of points in say labour-capital space at which the same quantity of output is produced for varying combinations of the inputs) is homogeneous of degree zero. Due to this, along rays coming from the origin, the slopes of the isoquants will be the same. Homothetic functions are of the form formula_26 where formula_27 is a monotonically increasing function (the derivative of formula_27 is positive (formula_29)), and the function formula_30 is a homogeneous function of any degree.