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Find the first partial derivatives of the function. f(x, t) = e−9t cos(πx)

Sagot :

Answer:

[tex]f_{x}(x,t) = -\pi e^{-9t} \sin{(\pi x)}[/tex]

[tex]f_{t}(x,t) = -9\cos{(\pi x)} e^{-9t}[/tex]

Step-by-step explanation:

We are given the following function:

[tex]f(x,t) = e^{-9t} \cos{(\pi x)}[/tex]

First derivatives:

We find the first derivatives in function of x and of t.

Function of x:

The exponential is only a function of t, so it is treated as a constant.

[tex]f_{x}(x,t) = e^{-9t} \frac{d}{dx](\cos{(\pi x)}) = -e^{-9t} \sin{(\pi x)} \frac{d}{dx}(\pi x) = -\pi e^{-9t} \sin{(\pi x)}[/tex]

Function of t:

Same logic as above, the cosine as treated as a constant.

[tex]f_{t}(x,t) = \cos{(\pi x)} \frac{d}{dt}(e^{-9t}) = \cos{(\pi x)} e^{-9t} \frac{d}{dt}(-9t) = -9\cos{(\pi x)} e^{-9t}[/tex]