Step by step
The question
Question: work out 5 times this matrix.
5[2; −1; 3]
A matrix is numbers in rows and columns, inside big brackets.
Each number in a matrix is called an entry.
1 Times every entry
5 in front means: every entry times 5.
We write 5 × in front of each one.
= [5 × 2; 5 × (−1); 5 × 3]
Careful!
Every entry gets times 5, in every row.
Not only the first one.
Careful: every entry × 5, every row
Now we work out each one.
5 times 2 is 10, and so on.
The answer: the column 10, −5, 15.
= [10; −5; 15]
2 Check
Let's check by dividing back: each entry divided by 5.
10 ÷ 5 = 2
−5 ÷ 5 = −1
15 ÷ 5 = 3
We get the first matrix back.
So the answer is right!
Let's look back.
First: times every entry.
Last: check.
Answer
= [10; −5; 15]