Posted by **mark11** on Friday, February 22, 2013 at 9:07pm.

use implicit differentiation to find dy/dx . Then evaluate the derivative function at the designated point.

log (xy)= 2; (4, 25)

- calculus -
**Steve**, Saturday, February 23, 2013 at 4:54am
log(xy) = 2

1/(xy) (y + xy') = 0

1/x + 1/y y' = 0

y' = -y/x

Or, going about it another way,

logx + logy = 2

1/x + 1/y y' = 0

y' = -y/x

So, plug in your numbers.

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