Step-by-step explanation:
length = width + 4
length×width = 77
using the first in the second equation
(width + 4)×width = 77
width² + 4width = 77
now, what square or squaring factors can create this ?
we are looking for (width + a)(width + b).
we know, this is
width² + (a+b)width + ab
so, what a, b can create 4 (the factor in our actual equation) ?
1, 3 and 2, 2, if we are only looking at whole numbers.
and which of the possibilities can we use to turn 77 into a square number ?
81 is only 4 away ...
2+2 = 4.
aha !
so, we can actually say our equation is
width² + 4width + 4 = 77 + 4
and then
(width + 2)² = 81
width + 2 = 9
width = 7 m
length = width + 4 = 7 + 4 = 11 m
