SOLUTION: The perimeter of rectangle is 28cm. Find the range of possible values of width of the rectangle if diagonal is less than 10cm

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Question 1087255: The perimeter of rectangle is 28cm. Find the range of possible values of width of the rectangle if diagonal is less than 10cm
Answer by ikleyn(52781) About Me  (Show Source):
You can put this solution on YOUR website!
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Let L be the length and W be the width.

Then we have L + W = 14; hence, L = 14-W and the diagonal is

sqrt%28W%5E2+%2B+%2814-W%29%5E2%29 < 10.

Square both sides:

W%5E2+%2B+%2814-W%29%5E2 < 100  ====>

W%5E2+%2B+196+-+28W+%2B+W%5E2 < 100  ====>

2W%5E2+-+28W+%2B+96 < 0  ====>

W%5E2+-+14W+%2B+48 < 0  ====>

the roots of the quadratic equation W%5E2+-+14W+%2B+48 = 0  are

W%5B1%2C2%5D = %2814+%2B-+sqrt%2814%5E2+-+4%2A48%29%29%2F2 = %2814+%2B-+sqrt%284%29%29%2F2 = %2814+%2B-+2%29%2F2  ====>

1)  W%5B1%5D = 8;   2)  W%5B2%5D = 6.


The width is between 6 and 7   (I accept that the width is the smaller dimension of the rectangle).


Answer.  At given conditions, the range of possible values of the width of a rectangle is the interval (6,7) 
         (accepting that the width is the smaller of the two dimensions of a rectangle).