## marigirl one year ago Differentiating : Differentiate A=l*w with respect to w

1. marigirl

how does it end up as $A=w*l$ $\frac{ dA }{ dw }=w*\frac{ dl }{ dw }+l$ Where did that +l come from?

2. anonymous

by the product rule

3. anonymous

dA/dw = w* dL /dw + d(w)/dw * L dA/dw = w* dL /dw + 1 * L

4. welshfella

l is a function of w

5. marigirl

thanks!

6. anonymous

you have to assume l is a function of w for that to make sense. otherwise you would end with dA/dw = L * 1, since L is a constant with respect to w

7. welshfella

yes

8. marigirl

can you please also explain what happens here $4r^2=l^2+w^2$ the model answers show that 4r^2 differentiates to zero

9. marigirl

again i am differentiating with respect to w

10. marigirl

@jayzdd