You can see figure as below. What do you find the difference? A corner is filleted here. So, how to create this corner?
1st way: You can make a circle contact with two line and then using Trim command.
2nd way: You can use Fillet command and do as following
step 1: Type F > Enter
step 2: Type R > Enter
step 3: Input Radius for Fillet corner
step 4: Select two lines that it create this corner
Select first object or [Undo/Polyline/Radius/Trim/Multiple]: R
Specify fillet radius <3.0000>: Input radius of value
Select first object or [Undo/Polyline/Radius/Trim/Multiple]: Click on first line
Select second object or shift-select to apply corner: Click on second line