So we have two chords intersecting each other. One of the angles in this intersection is equal to 86°. It's also important to note there are another two chords of equal measure that define a and c respectively. This means that arcs a and c have the same measure. What's more, these two arcs are related since they are also defined by the chords that made the 86° angle and the relation between them and this angle is:
[tex]86^{\circ}=\frac{a+c}{2}[/tex]
If we use the fact that a=c we get:
[tex]86^{\circ}=\frac{a+c}{2}=\frac{a+a}{2}=\frac{2a}{2}=a[/tex]
Then the value of a is 86° and the answer is option B.
