Question

The perimeter of the

rectangle is 14 m and
the area is 12 m2.
Calculate the length
of the rectangle
diagonal​

Answer 1

5

Explanation:

area of rectangle = l(ength)×w(idth)

perimeter = 2×l + 2×w

diagonal = sqrt(l² + w²) (Pythagoras)

l×w = 12. => l = 12/w

2×l + 2×w = 14

2×12/w + 2×w =14

12/w + w = 7

12 + w² = 7w

w² - 7w + 12 = 0

=> (after a little thinking and trying : what 2 numbers multiply to 12 and add to -7 ? -3 and -4

=> (w-3)×(w-4) = 0

so, we get 2 solutions for w : 3 and 4

that gives us 2 solutions for l : 4 and 3

so, one is 3 and the other 4. it does not matter which is which. length 4 and width 3 produce the same diagonal as length 3 and width 4.

diagonal = sqrt(l² + w²) = sqrt(16 +9) = sqrt(25) = 5