Step by step
The question
Question: find the value of 2x² − 3x + 1 when x = −2.
2x2 − 3x + 1
x = −2
1 Put the numbers in
We put −2 in place of x.
2x² means 2 times x².
So we write a times sign.
A negative number goes in brackets, so its minus stays with it.
= 2 × (−2)2 − 3 × (−2) + 1
2x² = 2 × x²
2 Powers
Powers come before times, minus and plus.
Order: ( ) → x² √ → × ÷ → + −
(−2)² means −2 times −2.
Minus times minus is plus.
(−2)2 = (−2) × (−2) = 4
That is 4.
= 2 × 4 − 3 × (−2) + 1
3 Times and divide
Times comes before minus and plus.
Times and divide: we go from left to right.
same kind: left → right
2 times 4 is 8.
= 8 − 3 × (−2) + 1
Times comes before minus and plus.
+ × − = −
Plus times minus is minus.
3 times 2 is 6.
So we get −6.
= 8 − (−6) + 1
4 Plus and minus
Plus and minus: we go from left to right.
Taking away a negative is the same as adding.
same kind: left → right
− (−) = +
So 8 − (−6) becomes 8 + 6.
= 8 + 6 + 1
8 plus 6 is 14.
= 14 + 1
14 plus 1 is 15.
= 15
So 2x² − 3x + 1 is 15 when x = −2.
Let's look back.
First: put the numbers in.
Then: powers.
Then: times and divide.
Last: plus and minus.
Answer
= 15