Question

Найти dz/du и dz/dv если z= x^2+2y^3
если x= u/v y= u*v

Answer 1

$z = {x}^{2} + 2 {y}^{3}$

$x = \frac{u}{v} \\ y = uv$

$\frac{dz}{du} = \frac{dz}{dx} \times \frac{dx}{du} + \frac{dz}{dy} \times \frac{dy}{du} \\$

$\frac{dz}{dv} = \frac{dz}{dx} \times \frac{dx}{dv} + \frac{dz}{dy} \times \frac{dy}{dv} \\$

$\frac{dz}{dx} = 2x \\ \frac{dz}{dy} = 6 {y}^{2}$

$\frac{dx}{du} = \frac{1}{v} \\ \frac{dy}{du} = v$

$\frac{dz}{du} = 2x \times \frac{1}{v} + 6 {y}^{2} \times v = \\ = \frac{2x}{v} + 6 {y}^{2} v$

$\frac{dx}{dv} = - u {v}^{ - 2} = - \frac{u}{v ^{2} } \\$

$\frac{dy}{dv} = u \\$

$\frac{dz}{dv} = 2x \times \times ( - \frac{u}{v ^{2} } ) + 6 {y}^{2} \times u = \\ = - \frac{2xu}{ {v}^{2} } + 6 {y}^{2} u$