14 Rectangle PORS has [PQ] of fixed length 20 cm, and [QR] increases in length at a constant rate of 2 cms . At what rate is the acute angle between the diagonals of the rectangle changing at the instant when [QR] is 15 cm long? 15 Triangle PQR is right angled at Q, and [PQ] is 6 cm long. [QR] increases in length at 2 cm per minute. Find the rate of change in QPR at the instant when [QR] is 8 cm long. other with constant speeds of