SOLUTION: The width of a painting is 4 inches less than the length, and the surface area is 320 square inches. Find the leng

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Question 134416: The width of a painting is 4 inches less than the length, and the surface area is 320 square inches. Find the leng
Answer by vleith(2983) About Me  (Show Source):
You can put this solution on YOUR website!
What is the formula for the area of a rectangle? Area = length * width.
Let length = l.
Given: width = length - 4, Area = 320
A+=+l%2Aw
A+=+l+%2A+%28l-4%29
320+=+l%5E2+-4l
0+=+l%5E2+-4l+-+320
0+=+%28l+%2B+16%29%28l+-+20%29
l = -16 , l = 20.
Since the length cannot be negative, the only solution that 'makes sense' is l = 20.
Check your answer. If l = 20, then width = 20-4 = 16. Is the area 320?