Miximizing the Area (calculus story problem)?

Question

i dont know what the primary and secondary equations are... i know the primary is the one being maxed or minned... but its still confusing...

A rancher has 200 feet of fencing with which to enclose two adjacent rectangular corrals. What dimensions should be used so that the enclosed area will be a maximum?

primary (i think): xy=a
secondary (maybe): 2xy = 200

Answer 1

Draw a picture.

Let x be the length of the side dividing the corrals. Let y be the length of the whole perpendicular to that.

Then the total area will be xy, no matter how the y pieces are divided between the two corrals. And the wire used is 2y +3x.

Convince yourself of all that, and then you surely know how to proceed.