Write the series 2+4+6+8++100 in sigma notation

We need to write the sum in this form:

So, we need to find an appropriate sequence, such that is the i-th even number.

You can easily check that this series is . In fact, you have

and so on. Finally, we have to observe that we want the first 50 elements of this sequence, since .

So, the sum can be written as

.25

step-by-step explanation:

b. 2 and 4

step-by-step explanation: