Question

Write the following sum using summation notation -2/5+3/6-4/7........11/14

Answer 1

Answer:

$\sum_{n=1}^{10}(-1)^n\left ( \frac{n+1}{n+4} \right )$

Step-by-step explanation:

Given: $\frac{-2}{5}+\frac{3}{6}-\frac{4}{7}+...+\frac{11}{14}$

To write: the given expression using summation notation

Solution:

Summation notation helps to write a long sum as a single expression.

In the summation notation, the variable $\sum$ is called the index of summation.

Let $x_1,x_2,x_3,...,x_n$ denote a set of n numbers.

Then in summation notation,

$x_1+x_2+x_3+...+x_n=\sum_{i=1}^{n}x_i$

$\frac{-2}{5}=(-1)^1\left ( \frac{1+1}{1+4} \right )\\\frac{3}{6}=(-1)^2\left ( \frac{2+1}{2+4} \right )\\\frac{-4}{7}=(-1)^3\left ( \frac{3+1}{3+4} \right )\\.\\.\\.\\\frac{11}{14}=(-1)^10\left ( \frac{10+1}{10+4} \right )\\\therefore \frac{-2}{5}+\frac{3}{6}-\frac{4}{7}+...+\frac{11}{14}=\sum_{n=1}^{10}(-1)^n\left ( \frac{n+1}{n+4} \right )$