Write the sum using summation notation, assuming the suggested pattern continues.
-9 - 3 + 3 + 9 + + 81

ANSWER

EXPLANATION

The given series

This is an arithmetic series with a common difference of

The first term of the series is:

The general term is given by:

The last term is 81

We can use this to determine the number of terms in the series.

The summation notation is:

because linear equations are a lot simpler than quadratics equations, and linear equations formula is a lot easier to memorize. that's why i think they're harder.