a * b = 40
2 a + 2 b = 28
so
a = 40/b
and then
2(40/b) + 2 b = 28
80 / b + 2 b = 28
40/b + b = 14
40 + b^2 = 14 b
b^2 - 14 b + 40 = 0
(b - 10)(b - 4) = 0
looks like 10 and 4 to me
A rectangular piece of plastic has a perimeter of 28 millimeters. Its area is 40 square millimeters. What are the dimensions of the piece of plastic?
5 answers
2 L + 2 W = 28 ... L + W = 14
L * W = 40
two numbers that add to 14 and multiply to 40 ...
L * W = 40
two numbers that add to 14 and multiply to 40 ...
L + L + w + w = 28
L(w) = 40
Solve for one variable and sub it back into an original and solve for the other variable.
hint: you may wish to consider what times what is 40... as a starting point for an educated guess : )
L(w) = 40
Solve for one variable and sub it back into an original and solve for the other variable.
hint: you may wish to consider what times what is 40... as a starting point for an educated guess : )
7.1 millimetres
5 and 9