SOLUTION: The Mona Lisa is a famous painting by Leonardo da Vinci. The painting is 30 inches by 21 inches. It is surrounded by a frame of uniform thickness whose area (not including the cent

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Question 1156439: The Mona Lisa is a famous painting by Leonardo da Vinci. The painting is 30 inches by 21 inches. It is surrounded by a frame of uniform thickness whose area (not including the center) is 756 inches squared. Find the thickness of the frame.
Found 2 solutions by josgarithmetic, ikleyn:
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
the uniform "thickness", u

%2830%2B2u%29%2821%2B2u%29-30%2A21=756
Simplify, and continue from this.

Answer by ikleyn(52786) About Me  (Show Source):
You can put this solution on YOUR website!
.


(21+2x)*(30+2x) - 21*30 = 756


60x + 42x + 4x^2 = 756


4x^2 + 102x - 756 = 0


x^2 + 51x - 378 = 0


x%5B1%2C2%5D = %28-51+%2B-+sqrt%28%28-51%29%5E2%2B4%2A1%2A378%29%29%2F%282%2A2%29 = %28-51+%2B-+75%29%2F4.


Negative root does not work.  The positive root  x = %28-51+%2B+75%29%2F4 = 6 is the solution to the problem.


ANSWER.  6 inches.

Solved.

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If you want to see many other similar solved problems, look into the lessons
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in this site.

Also,  you have this free of charge online textbook in ALGEBRA-I in this site
    - ALGEBRA-I - YOUR ONLINE TEXTBOOK.

The referred lesson is the part of this online textbook under the topic
"Dimensions and the area of rectangles and circles and their elements".

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Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson

to your archive and use it when it is needed.