The length of a rectangle exceeds its breadth  by 8cm. If the length was halved and the breadth increased by 6cm, the area would be decreased by 36 cm^2. Find the length andperimeter of the...

The length of a rectangle exceeds its breadth  by 8cm. If the length was halved and the breadth increased by 6cm, the area would be decreased by 36 cm^2. Find the length andperimeter of the original rectangle.

Expert Answers
mvcdc eNotes educator| Certified Educator

We let the length be represented by Land the breadth by B.

The length of the rectangle exceeds its breadth by 8cm. This can be translated to a mathematical expression:

L = B + 8

Now, the length was halved and the breadth was increased by 6. This means that the new length is L/2 and the new breadth is B + 6. 

The area of the original rectangle is:

`A_(old) = L *B = (B+8)*B = B^2 + 8B`

The area of the new rectangle is:

`A_(n e w) = L/2 * (B+6) = (B+8)/2 * (B+6) = (B^2 + 14B + 48)/2`

Now, we know that the new rectangle has a lower area then the old:

`A_(old) - A_(n e w) = 36`

This means that:

`B^2 + 8B - (B^2 + 14B + 48)/2 = 36`

This is just a quadratic equation that can easily be solved. First, we simplify it:

`2B^2 + 16B - B^2 - 14B - 48 = 72`

`B^2 + 2B - 120 = 0`

Using the quadratic formula:

`(-2 pm sqrt(2^2 - 4*1*-120))/2`

`(-2 pm sqrt(484))/2`

The roots are 10 and -12

Hence, `B=10` (the other root is negative, and hence, is not a reasonable answer, since lengths are positive).

We know that in the original rectangle, the length is 8cm more than B. Hence, L = 18cm. 

The perimeter of the original rectangle then, is P = 18*2 + 10*2 = 56 cm.