آلاخونه

hey
aval masahat ro bar asas x,y benevis ke mishe S=2xy bad be tabe x bede v y khroji daryaft kon dar akhr oon ro bezar jaye y ya x

masaln jvab in mishe
S=2xy
y=4-x^2====>
S=2.x. (4-x^2 )
S=8x-4x3