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9. The length of a rectangle is 3 cm longer than twice the width. If the area of the rectangle is 65 cm2,

find its length and the width.

User Leemour
by
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1 Answer

3 votes

Answer:

length: 13 cm

width: 5 cm

Explanation:

You may be aware that 65 = 5×13. We note that 13 is 3 more than twice 5, so these are the dimensions of the rectangle:

5 cm wide; 13 cm long

__

If you want so solve this algebraically, you can let w represent the width. Then the length is 2w+3 and the area is ...

A = LW

65 = (2w+3)(w)

In standard form, this equation is ...

2w^2 +3w -65 = 0

To factor this, you look for factors of 2×(-65) = -130 that have a sum of 3. Those would be ...

-130 = (-10)(13)

Then the factored equation is ...

2w^2 +13w -10w -65 = 0

w(2w+13) -5(2w+13) = 0

(w -5)(2w +13) = 0 ⇒ w = 5, -13/2

The positive solution makes sense in this problem, so ...

width = 5 cm

length = 2(5) +3 = 13 cm

User Matt Accola
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