Find the diagonal of a rectangle whose length is 16 cm and area is 192 sq.cm.

Let PQRS be the rectangle.
Let length be PQ = 16 cm
Area of rectangle = Length × Breadth
Area of rectangle PQRS = PQ×QR
192 = 16×QR
QR = 192/16 = 12cm
Now in PQR , Q = 90˚ [Angles of a rectangle are 90˚]
PR² = PQ²+QR² [Pythagoras theorem]
PR² = 16²+12²
PR² = 256+144 = 400
PR = 20
Hence the diagonal of the rectangle is 20cm long.