Step by step
The question
Question: find the value of 4x − 3y when x = 2 and y = −3.
4x − 3y
x = 2, y = −3
1 Put the numbers in
We put 2 in place of x and −3 in place of y.
4x means 4 times x.
So we write a times sign.
A negative number goes in brackets, so its minus stays with it.
= 4 × 2 − 3 × (−3)
4x = 4 × x
2 Times and divide
Times comes before minus.
Times and divide: we go from left to right.
Order: ( ) → x² √ → × ÷ → + −
same kind: left → right
4 times 2 is 8.
= 8 − 3 × (−3)
Times comes before minus.
+ × − = −
Plus times minus is minus.
3 times 3 is 9.
So we get −9.
= 8 − (−9)
3 Plus and minus
Taking away a negative is the same as adding.
− (−) = +
So 8 − (−9) becomes 8 + 9.
= 8 + 9
8 plus 9 is 17.
= 17
Careful!
Many people go from left to right and get −15.
But times and divide come before plus and minus.
Careful: not 4 × 2 − 3 × (−3) = −15 ✗
So 4x − 3y is 17 when x = 2 and y = −3.
Let's look back.
First: put the numbers in.
Then: times and divide.
Last: plus and minus.
Answer
= 17