Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A signal generator in a school laboratory produces a voltage volts, where is the time in seconds. The area between the voltage graph and the time axis has the unit volt second. A technician records the signal from to seconds, which is one and a half cycles of the wave. She wants two numbers from the record. The first is the net area, which counts the part of the graph below the time axis as negative. The second is the total area, which counts every part of the graph as positive. The net area is useful when the direction of the voltage matters, and the total area is useful when only its size matters. The record is used to test a new data logger, and the logger must report both quantities correctly. The technician will check its output against her own hand calculation. Find both numbers, in volt seconds.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The zeros. when , so . The interval splits into three pieces.
Step 2. The antiderivative. . Then , , and .
Step 3. The three pieces. The pieces are , then , then volt seconds.
Step 4. The two numbers. The net area is volt seconds. The total area is volt seconds.
Answer: net area volt seconds, total area volt seconds. The two cycles of the wave that cancel in the net area still count in the total.
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The integral gives a signed area. For the total area, find the zeros of inside the interval, integrate over each piece and add the absolute values of the results.