# Thread: Need help finding a linear approximation

1. ## Need help finding a linear approximation

Find the linear approximation of f(x,y)=((x^2+y^2)^(1/2)) and use it to approximate the number ((3.1)^2+(3.9)^2))^(1/2)

2. ## Re: Need help finding a linear approximation

Hey allstar2.

Can you show us what you have tried? (Hint: The linearization involves the Jacobian matrix).

3. ## Re: Need help finding a linear approximation

Of course you have the nearby point $(3^2+4^2)^{\frac{1}{2}}=5$.

You just need the partial derivatives with respect to x and y, and then you can use the chain rule for 2 variables.

- Hollywood