Example
The cookie factory's production function is `q \left( c, s \right) = K L^2`. The marginal rate of technical substitution is
$$ MRTS = - \frac{MP_L\left( K, L\right)}{MP_K \left( K, L \right)} = - \frac{2 K L}{L^2} = -\frac{2 K}{L} $$Question
The production function is `q (K, L) = K^{2} L^{89}`.
Calculate the marginal rate of technical substitution in function of K and L.
The marginal product of labor is
$$
MP_L = \frac{dq(K, L)}{dL} = 89 K^{2} L^{89 - 1} = 89 K^{2} L^{88}
$$
The marginal product of capital is
$$
MP_K = \frac{dq(K,L)}{dK} = 2 K^{2 - 1} L^{89} = 2 K^{1} L^{89}
$$
Therefore, the marginal rate of technical substitution is
$$
MRTS = - \frac{MP_L}{MP_K} = - \frac{89 K^2 L^{88}}{2 K^1 L^89} = - \frac{89 K}{2 L}
$$