The tangent of a circle always form 90 degree angle with the radius. So measure of angle ABO and angle ACO is 90 degrees each.
The sum of angles of a quadilateral is 360 degrees. So,
![\angle BOC+\angle ABO+\angle ACO+\angle BAC=360](https://img.qammunity.org/2023/formulas/mathematics/college/kpnnx0zo3nz1i89palkvikcfs7wtvr6k5n.png)
Substitute the measures of angles in the equation to obtain the measure of angle BOC.
![\begin{gathered} \angle BOC+90+90+90=360 \\ \angle BOC=360-270 \\ =90 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/16pi6emiaymo24ebdrtk1ifn5hjhf8jvtl.png)
Thus, measure of angle BOC is 90 degrees.