When the length of each side of a square is decreased by 20cm, its area is decreased by 5600cm^2. How do you find the length of a side of the square before the decrease?

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Answer 1 · 2016-08-10T15:25:55

Write a systems of equations. Let #l# be the side length of the square and #A# the area. So, we can say:

#l^2 = A#

#(l - 20)^2 = A - 5600#

We are looking to find #l#. I think in this case substitution would be easiest.

#(l - 20)^2 = l^2 - 5600#

#l^2 - 40l + 400 = l^2 - 5600#

#l^2 - l^2 - 40l + 400 + 5600 = 0#

#-40l + 6000 = 0#

#-40l = -6000#

#l = 150#

Hence, the initial length was #150# centimetres.

Hopefully this helps!