Science:Math Exam Resources/Courses/MATH152/April 2016/Question A 25/Solution 1

We follow the hint and apply Kirchoff's current law to the top node.

The current coming into the node from the left is is $i_{1}$, the current entering the node from the bottom is $I$, and the current leaving the node from the right is $i_{2}$. We therefore have $i_{1}+I=i_{2}$. Solving for $I$ gives $I=i_{2}-i_{1}$.

Answer: $\color {blue}I=i_{2}-i_{1}$