Let z=2x+5y−−−−−−√

. Then:

The rate of change in z
at (2,4)
as we change x
but hold y
fixed is
, and

The rate of change in z
at (2,4)
as we change y
but hold x
fixed is

1 answer

To find the rate of change in z at (2,4) as we change x but hold y fixed, we take the partial derivative of z with respect to x and evaluate it at (2,4).

The partial derivative of z with respect to x is given by:

∂z/∂x = 2

So, the rate of change in z at (2,4) as we change x but hold y fixed is 2.

To find the rate of change in z at (2,4) as we change y but hold x fixed, we take the partial derivative of z with respect to y and evaluate it at (2,4).

The partial derivative of z with respect to y is given by:

∂z/∂y = 5/2√(2x+5y)

Plugging in the values of x=2 and y=4 into the partial derivative, we get:

∂z/∂y = 5/2√(2(2)+5(4)) = 5/2√(4+20) = 5/2√24 = 5/2√6

So, the rate of change in z at (2,4) as we change y but hold x fixed is 5/2√6.