SME
Grade 9 Math · Problem type
Evaluate a quadratic
Use this for “f(x) = 2x² − 3x + 1. Find f(−2).”
Chart
f(−2) = 15
This is an example. Type your own values to start a new problem.
f(x)
=
a
x²
+
(
b
)
x
+
c
f(
)
=
y
Formulas
y
=
a
×
x
2
+
b
×
x
+
c
15
=
2
×
(−2)
2
+
(−3)
×
(−2)
+
1
Assumptions
•
Put the input in brackets wherever x is: 2(−2)², not 2 × −2².
•
Square first, then multiply, then add and subtract.
•
Two inputs can give the same output, so here the output is only worked out.
Step-by-step
WE KNOW
x = −2, a = 2, b = −3, c = 1
FIND
output f(x) (y)
Step 1 · Find output f(x): y
Use y = a × x² + b × x + c
Put
the
input
in
for
x
,
then
square,
multiply
and
add
in
that
order.
y
=
2
×
(−2)
2
−
3
×
(−2)
+
1
y
=
2
×
4
−
3
×
(−2)
+
1
y
=
8
+
6
+
1
y
=
15
Check
Put the numbers back in. Both sides should match.
15
=
2
×
(−2)
2
−
3
×
(−2)
+
1
✓
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