In one question an ellipse was drawn in pv graph and we have to calculate the work done.proof for finding area of ellipse is in the topic area under curve in in class 11???
Area is pi*a*b in which a and b are length of minor answers major axis respectively ..
I studied it in basic mathematics used in physics in 11th only
This link has several methods for proving the area of Ellipse @Sarju_Panchal1
See if this helps
Area of ellipse is also proved in Class 12 NCERT Mathematics.