Answer:
Length= 19cm
Width= 9cm
Explanation:
let the length of the rectangle be L cm and its width be W cm.
Perimeter of rectangle= 56cm
2L +2W= 56
L +W= 56 ÷2
L +W= 28
L= 28 -W -----(1)
Area of rectangle= length ×width
LW= 171 -----(2)
Susbt. (1) into (2):
W(28 -W)= 171
28W -W²= 171 (expand)
W² -28W +171= 0 (bring everything to one side)
(W -19)(W-9)= 0 (factorise)
W-19=0 or W-9=0
W= 19 or W= 9
Subst into (1):
L=28 -19 or L= 28 -9
L=9 or L= 19
Since we usually take the longer side of the rectangle to be its length, L= 19 and hence W=9.
Therefore its length is 19cm and its width is 9cm.