Question 1193332
<pre>
{{{drawing(400,4000/19,-2,17,-2,8,

locate(5.8,6.85,4x+5), locate(6.5,0,6x-3),

line(0,0,15,0), line(15,0,9,6),line(9,6,4,6),line(4,6,0,0),line(2,3,12,3),

locate(0,0,C), locate(14.8,0,D), locate(8.8,6.85,A), locate(3.95,6.85,B), locate(1.5,3.5,N), locate(12.2,3.5,M)   )}}} 

The midline of a trapezoid is the average of the two parallel sides:

{{{MN}}}{{{""=""}}}{{{(AB+DC)/2}}}

{{{MN}}}{{{""=""}}}{{{((4x+5)+(6x-3))/2}}} 

{{{MN}}}{{{""=""}}}{{{(4x+5+6x-3)/2}}}

{{{MN}}}{{{""=""}}}{{{(10x+2)/2}}}  

{{{MN}}}{{{""=""}}}{{{(2(5x+1))/2}}}  

{{{MN}}}{{{""=""}}}{{{(cross(2)(5x+1))/cross(2)}}} 

{{{MN}}}{{{""=""}}}{{{5x+1}}} 

Edwin</pre>