SOLUTION: If the sides of a square are lengthened by 5cm, the area becomes 81cm^2. Find the length of a side of the original square.

Algebra ->  Length-and-distance -> SOLUTION: If the sides of a square are lengthened by 5cm, the area becomes 81cm^2. Find the length of a side of the original square.      Log On


   

Question 157330: If the sides of a square are lengthened by 5cm, the area becomes 81cm^2. Find the length of a side of the original square.
Answer by jojo14344(1513) About Me  (Show Source):
You can put this solution on YOUR website!
Let s= original side
s%2B5= lengthened by 5 cm
A%5Bnew%5D=81cm%5E2
So, A%5Bnew%5D=%28s%2B5%29%5E2 ---------------> working eqn
81=s%5E2%2B10s%2B25
s%5E2%2B10s%2B25-81=0
s%5E2%2B10s-56=0, factor out, perfect square
%28s%2B14%29%28s-4%29=0
2 values: s=-14 ----------> don't use
s=4cm ---------------------> original side
In doubt? go back working eqn,
81=%28s%2B5%29%5E2
81=%284%2B5%29%5E2
81=9%5E2
81=81
thank you,
Jojo