Question

I need help with summation notation. Look at picture

Answer 1

Answer:

$=18$

Step-by-step explanation:

$\sum _{j=1}^33j$

Apply the constant multiplication rule:

$=3\cdot \sum _{j=1}^3j$

$\sum _{j=1}^3j$

Apply sum formula:

$=\frac{1}{2}\cdot \:3\left(3+1\right)$

$\frac{1}{2}\cdot \:3\left(3+1\right)$

$=3\cdot \:4\cdot \frac{1}{2}$

$=\frac{1\cdot \:3\cdot \:4}{2}$

$=\frac{12}{2}$

$=6$

$=3\cdot \:6$

$=18$