This partial production function shows how output increases as more labour is being employed while the capital stock remains fixed. Its graph is obtained by placing a vertical cut through the 3D production function parallel to the axis that measures labour.

The slope of the partial production function measures how much output is gained by a given small increase of labour. This slope is called the marginal product of labour. The two tangency lines measure this marginal product of labour at L₁ and L₂. They indicate that the marginal product of capital becomes smaller and smaller as more and more work-hours are being employed.

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