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Quadratic & Polynomial Equations for CAT: Formulas, Weightage & Question Types

Roots, the discriminant, symmetric expressions and quadratics in disguise.

Quadratic & Polynomial Equations formula sheet

Everything CAT needs from Quadratic & Polynomial Equations, in one place. Bookmark it for revision; the lesson in the app explains where each line comes from and when to reach for it.

Everything for this chapter, in one place. ax2+bx+c=0ax^2+bx+c=0, with a≠0a \neq 0, roots α\alpha and β\beta.

Roots and the discriminant

Rootsx=−b±D2ax = \dfrac{-b \pm \sqrt{D}}{2a}
DiscriminantD=b2−4acD = b^2 - 4ac

Nature of the roots — assumes a,b,ca,b,c are real

ConditionRoots
D>0D > 0two distinct real roots
D=0D = 0two equal real roots (one repeated)
D<0D < 0no real roots
D>0D > 0 and a perfect square, a,b,ca,b,c rationalroots are rational
D>0D > 0, not a perfect square, a,b,ca,b,c rationalroots are irrational conjugates p±qp \pm \sqrt{q}

Sum and product — use these instead of solving

α+β\alpha + \beta−ba-\dfrac{b}{a}
αβ\alpha\betaca\dfrac{c}{a}
α−β\alpha - \beta±Da\pm\dfrac{\sqrt{D}}{a}
(α−β)2(\alpha-\beta)^2(α+β)2−4αβ(\alpha+\beta)^2 - 4\alpha\beta
α2+β2\alpha^2 + \beta^2(α+β)2−2αβ(\alpha+\beta)^2 - 2\alpha\beta
α3+β3\alpha^3 + \beta^3(α+β)3−3αβ(α+β)(\alpha+\beta)^3 - 3\alpha\beta(\alpha+\beta)
1α+1β\dfrac{1}{\alpha} + \dfrac{1}{\beta}α+βαβ=−bc\dfrac{\alpha+\beta}{\alpha\beta} = -\dfrac{b}{c}
1α2+1β2\dfrac{1}{\alpha^2} + \dfrac{1}{\beta^2}(α+β)2−2αβ(αβ)2\dfrac{(\alpha+\beta)^2 - 2\alpha\beta}{(\alpha\beta)^2}
Equation from its rootsx2−(α+β)x+αβ=0x^2 - (\alpha+\beta)x + \alpha\beta = 0

Sign, maximum and minimum

ConditionResult
Vertex is atx=−b2ax = -\dfrac{b}{2a}
Value there−D4a=4ac−b24a-\dfrac{D}{4a} = \dfrac{4ac-b^2}{4a}
a>0a>0that value is the minimum; curve opens upward
a<0a<0that value is the maximum; curve opens downward
a>0a>0 and D<0D<0f(x)>0f(x) > 0 for every real xx
a<0a<0 and D<0D<0f(x)<0f(x) < 0 for every real xx

Common roots — for a1x2+b1x+c1=0a_1x^2+b_1x+c_1=0 and a2x2+b2x+c2=0a_2x^2+b_2x+c_2=0

Both roots shareda1a2=b1b2=c1c2\dfrac{a_1}{a_2} = \dfrac{b_1}{b_2} = \dfrac{c_1}{c_2}
One root sharedsubtract the scaled equations to eliminate x2x^2, then solve for xx

Cubic ax3+bx2+cx+d=0ax^3+bx^2+cx+d=0 with roots α,β,γ\alpha,\beta,\gamma

α+β+γ\alpha+\beta+\gamma−ba-\dfrac{b}{a}
αβ+βγ+γα\alpha\beta + \beta\gamma + \gamma\alphaca\dfrac{c}{a}
αβγ\alpha\beta\gamma−da-\dfrac{d}{a}

The 6 Quadratic & Polynomial Equations question types CAT repeats

Past CAT papers return to the same few shapes. Learn to recognise them and most questions become a known routine. Beyond these, CAT has asked 8 rarer one-off shapes here.

  1. 01

    Control the discriminant

  2. 02

    Symmetric in the roots

  3. 03

    A sum of squares equals zero

  4. 04

    Substitute, then it is quadratic

  5. 05

    A word problem that becomes a quadratic

  6. 06

    Maximum or minimum

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Quadratic & Polynomial Equations in CAT: quick answers

How many Quadratic & Polynomial Equations questions come in CAT Quant?
About 1.7 questions in a 22-question Quant section, worth roughly 5 marks. Quadratic & Polynomial Equations appeared in 23 of the 24 CAT papers from 2017 to 2025, 37 questions in all, which ranks it 1 of 25 Quant chapters.
Are Quadratic & Polynomial Equations questions in CAT MCQ or TITA?
32% of the Quadratic & Polynomial Equations questions asked since 2017 were TITA (type in the answer, no negative marking). The rest were multiple choice.
What types of Quadratic & Polynomial Equations questions does CAT ask?
CAT keeps returning to 6 question shapes in Quadratic & Polynomial Equations: Control the discriminant; Symmetric in the roots; A sum of squares equals zero; Substitute, then it is quadratic; A word problem that becomes a quadratic; Maximum or minimum.

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