application of derivatives

[fossil mantle]

Where does your work start and end

Can you label more?

[sharp idol]

1st mistake

$x^2 + y^2 = 4r^2$

[forest panther]

Invicible

[sharp idol]

1st you need to prove area is max when x=y
then its obvious that x^2+y^2 = 4r^2 => 2x^2 = 4r^2=> x=√2 r