Exams
Courses
Pricing
About
FAQ
← Scholarship Calculus
Bridge
Equations, logs and inequalities
Free
Cubic equations: roots in arithmetic progression
mathematical
The equation
2
x
3
−
9
x
2
+
k
x
−
6
=
0
2x^3 - 9x^2 + kx - 6 = 0
2
x
3
−
9
x
2
+
k
x
−
6
=
0
has three real roots that form an arithmetic sequence.
Facts you may need
For
2
x
3
−
9
x
2
+
k
x
−
6
2x^3 - 9x^2 + kx - 6
2
x
3
−
9
x
2
+
k
x
−
6
: sum of roots
=
9
2
= \frac92
=
2
9
, product
=
3
= 3
=
3
— Vieta's formulas.
Factor theorem
— A known root gives a linear factor.
(a)
Find the value of
k
k
k
.
Strategy hint
Answer
Worked solution
(b)
Find the three roots.
Strategy hint
Answer
Worked solution
▸ Review notes: key idea, common errors, tips
← Roots of unity and exact trigonometric values
Exponential equations reducible to quadratics; parameter analysis →