Answer:
2
Step-by-step explanation:
<h2><u>the midpoint formula :</u></h2>
(x1 +x2) /2 , (y1 + y2)/2
<h3>finding the midpoint of AC.</h3>
a's coordinates are : ( 0,0) -- where 0 (left) is the x axis , 0 (right) is the y axis
c's coordinates are : ( a,a)-- where a (left) is the x axis , a (right) is the y axis
( a - 0)/2 , (a - 0)/2
=a/2 , a/2
<u>hence the value in the green box is 2 </u>