Step by step
The question
Question: find the value of 3a² − b when a = 2 and b = 5.
3a2 − b
a = 2, b = 5
1 Put the numbers in
We put 2 in place of a and 5 in place of b.
3a² means 3 times a².
So we write a times sign.
= 3 × 22 − 5
3a² = 3 × a²
2 Powers
Powers come before times and minus.
Order: ( ) → x² √ → × ÷ → + −
2² means 2 times 2.
22 = 2 × 2 = 4
That is 4.
= 3 × 4 − 5
3 Times and divide
Times comes before minus.
3 times 4 is 12.
= 12 − 5
4 Plus and minus
12 minus 5 is 7.
= 7
So 3a² − b is 7 when a = 2 and b = 5.
Let's look back.
First: put the numbers in.
Then: powers.
Then: times and divide.
Last: plus and minus.
Answer
= 7