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April 30th, 2012, 03:48 AM  #1 
Newbie Joined: Apr 2012 Posts: 1 Thanks: 0  Finding altitude of a part of trapezoid with given area...
Is there a formula for this one? Please help 
April 30th, 2012, 03:58 AM  #2 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 14,597 Thanks: 1038  Re: Finding altitude of a part of trapezoid with given area.
Extend to right to form right triangle. Then work with similar right triangles. 
April 30th, 2012, 01:01 PM  #3 
Global Moderator Joined: May 2007 Posts: 6,805 Thanks: 716  Re: Finding altitude of a part of trapezoid with given area.
y = ax + b. When x = 0, y = 10, when x = 10, y = 5. Plug into equation and solve for a and b. 
April 30th, 2012, 07:13 PM  #4 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,958 Thanks: 1146 Math Focus: Elementary mathematics and beyond  Re: Finding altitude of a part of trapezoid with given area.
Area of a trapezoid , where is height and and are the parallel sides. So we've got as the area of the blue part and as area of the red part, where is the width of the blue area and is the length of the segment between the blue and red areas. From the first equation, Substitute that into the second equation, 
May 1st, 2012, 03:57 AM  #5 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 14,597 Thanks: 1038  Re: Finding altitude of a part of trapezoid with given area.
Extending to form right triangle: triangle has legs 10 and 20; total area 100; new red area = 10023 = 77: so y(20  x) = 154 [1] Similar right triangles means y / (20  x) = 10/20: so x = 20  2y [2] [2] in [1]: y[20  (20  2y)] = 154; solve: y = SQRT(77) 

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altitude, area, finding, part, trapezoid 
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