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2014-06-19T11:34:24+08:00

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The square of number is decreased by 15. This value is twice the original number. Find the number(s). The answer is:

x-15=2x
x-2x-15=0
(x-5)(x+3)=0
x=5x  x=(-3)
2 4 2
You missed the ^2 :)
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2014-06-19T12:24:50+08:00

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Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
The most common problems involving quadratic equations are finding the dimensions when the area is given.

Example:

Find the dimensions of a rectangular textbook whose length is 10cm longer than its width and covers an area of 375 cm².

Solution:

Let x be the width of the textbook
      x+10 be the length of the textbook

A = width·length
375 = x (x+10)
375 = x² +10x
    0 = x² +10x -375
    0 = (x+25) (x-15) 
x+25 = 0     ;     x-15 = 0
     x = -25    ;     x = 15           (use x=15 because dimensions may never be negative)

Answer :
              Width = 15 cm

              Length = 25 cm        (from x+10)
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