Answer: The dimensions are 7cm and 3cm.
Explanation:
The following equation can be deduced from the question
L × W = 21 ....... i
2L + 2W = 20 .......... ii
Divide equation ii through by 2
(2L + 2W = 20) / 2
L + W = 10 ....... iii
From equation iii
L = 10 - W ......... iv
Put equation iv into I
L × W = 21
(10 - W) × W = 21
10W - W² = 21
W² - 10W + 21 = 0
W² - 7W - 3W + 21 = 0
W(W - 7) - 3(W - 7) = 0
W - 3 = 0
W = 0+3
W = 3 centimeter
Since,
Length × Width = 21
Length = 21/3
Length = 7 centimeters
The dimensions are 7cm and 3cm.