Question

A rectangle initially has dimensions 6 cm by 7 cm. All sides begin increasing in length at a rate of 4 cm/s. At what rate is the area of the rectangle increasing after 22 s​?

Answer 1

You can make a A.P. of sides at each second;

for 1st side, 6,10,14.....

here, a = 6, d=4, n=22, an =?

an= a+(n-1)d

an=6+(22-1)4

an =6+84

an = 90

For 2nd side, 7,11,15...

Here, a=7,d=4,n=22,an=?

an = 7+(21)4

an=91

dimensions after 22 sec = 90cm* 91 cm

Area would be equal to 8190 cm²