Question 1019335
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http://prntscr.com/a23h3z
So, I'm aware I have to use the distance formula. 
For (-b,c) and (a,0) I got [sqroot (a+b)^2+(D-c)^2)] after simplifying it, but I don't know how to simplify any further. The same thing foes for [sqroot (-a-b)+(0-c)]. I don't know how to simplify these with the distance formula like I do if they were numbers because they're coordinates. A little help and explanation would be nice. 
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The answer is {{{sqrt((a+b)^2+c^2)}}}.

For the solution, first draw the diagonal from (-a,0) to (b,c).

Then draw the perpendicular from the point (b,c) to the base of the trapezoid.

You will get a right-angled triangle with the horizontal leg length (a + b) and the vertical leg length c. 

The diagonal of the trapezoid is the hypotenuse of this triangle,

and its length is {{{sqrt((a+b)^2+c^2)}}}.

Same is the length of the other diagonal.
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