Step by step
The question
Question: find the value of 2a² − 3b when a = 4 and b = 5.
2a2 − 3b
a = 4
b = 5
1 Put the numbers in
2a² means 2 times a².
So we write a times sign.
2a² = 2 × a²
We put 4 in place of a and 5 in place of b.
= 2 × 42 − 3 × 5
2 Powers
Everyone uses the same order, so we all get the same answer.
Powers come before times and minus.
Order: Powers → × ÷ → + −
4² means 4 times 4.
42 = 4 × 4
= 16
That is 16.
= 2 × 16 − 3 × 5
3 Times and divide
Times comes before minus.
2 times 16 is 32.
= 32 − 3 × 5
Times comes before minus.
3 times 5 is 15.
= 32 − 15
4 Plus and minus
32 minus 15 is 17.
= 17
So 2a² − 3b is 17 when a = 4 and b = 5.
Let's look back.
First: put the numbers in.
Then: powers.
Then: times and divide.
Last: plus and minus.
Answer
= 17