A circular metal plate expands under heating so that its radius increases by 2%. Find the approximate increase in the area of the plate, if the radius of the plate before heating is 10 cm.
Let the radius of the plate 10cm.
Radius increases by 2% by heating
∴ After increment = 
Change in radius dr = 0.2
∴ New radius = 10+0.2 = 10.2cm
Area of circular plate = A=πr2
∴ Change in Area = 
⇒ 
⇒ 
⇒ 
2