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Lesson 12 of 13

8 min

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What the zeros of a polynomial say about its coefficients
IdeaHow it goes
The zeroAn input where the value is 0. One substitution tests it.
Brackets(x − p)(x − q) has zeros p and q. Each bracket is 0 at its own zero.
The curveThe zeros are the x-coordinates where the curve meets the x-axis.
The sumIf ax² + bx + c has zeros, their sum is −b/a.
The productIf ax² + bx + c has zeros, their product is c/a.
BackwardsZeros with sum S and product P give x² − Sx + P.
The signsIf zeros exist, a positive product means they share a side. A negative product means they sit on opposite sides.
Values from S and Pα² + β² = S² − 2P. And 1/α + 1/β = S/P.
The cubicα + β + γ = −b/a. αβ + βγ + γα = c/a. αβγ = −d/a.

Which input is a zero of x² − 7x + 12?

  • 3
  • −3
  • 7

p(x) = (x + 4)(x − 6). What are its zeros?

  • −4 and 6
  • 4 and −6
  • 4 and 6

A curve touches the x-axis at one point and turns back. How many zeros does it show?

  • 2, one from each side
  • 0
  • 1

What is the sum of the zeros of 3x² − 12x + 5?

  • −4
  • 4
  • 12

What is the product of the zeros of 2x² + 6x − 8?

  • −8
  • −4
  • 4

Which quadratic has zeros with sum 6 and product 8?

  • `x² − 6x + 8`
  • `x² + 6x + 8`
  • `x² − 8x + 6`

For x² + 9x + 14, we have S = −9 and P = 14. What do the zeros look like?

  • One on each side of 0
  • Both negative
  • Both positive

α and β are the zeros of x² − 6x + 4. What is α² + β²?

  • 36
  • 44
  • 28

What is the product of the zeros of x³ + 2x² − 5x − 6?

  • −6
  • −5
  • 6

Open Chapter 2, Polynomials, in your NCERT book. Read its solved examples as walks you have already taken.

Next: Pair of Linear Equations in Two Variables. Two equations, two letters, one shared answer.

Reveal every answer to finish this lesson.