Aptitude - Area - Discussion
Discussion Forum : Area - General Questions (Q.No. 9)
9.
The diagonal of a rectangle is 41 cm and its area is 20 sq. cm. The perimeter of the rectangle must be:
Answer: Option
Explanation:
l2 + b2 = 41.
Also, lb = 20.
(l + b)2 = (l2 + b2) + 2lb = 41 + 40 = 81
(l + b) = 9.
Perimeter = 2(l + b) = 18 cm.
Discussion:
15 comments Page 2 of 2.
Mishi said:
1 decade ago
I can't understand this. Please someone explain this clearly?
Abhi said:
1 decade ago
How did you took root of 41 there?
Sabir said:
1 decade ago
As u know hypotenuse^2 = base^2+ alt^2
Since √41 is the diagonal
l^2 + b^2 = 41
Also lb = 20 (Since area = 20)
Now we have to find 2(l+b) (Perimeter)
So remember the formula (a+b)^2 = a^2 + 2ab + b^2
So (l+b)^2 = l^2 + b^2 + 2lb
= 41+(2*20)
=81
Therefore, l+b = 9
Now perimeter = 2(l+b)
= 2*9
=18 cm
:)
Since √41 is the diagonal
l^2 + b^2 = 41
Also lb = 20 (Since area = 20)
Now we have to find 2(l+b) (Perimeter)
So remember the formula (a+b)^2 = a^2 + 2ab + b^2
So (l+b)^2 = l^2 + b^2 + 2lb
= 41+(2*20)
=81
Therefore, l+b = 9
Now perimeter = 2(l+b)
= 2*9
=18 cm
:)
(1)
Mmmm said:
1 decade ago
How did you take 40 there ?
Krish said:
1 decade ago
How 81 came?
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