Find the values of y for which the expression \(\frac{y^2 - 9y + 18}{y^2 + 4y - 21}\) is undefined

  • A 6, -7
  • B 3, -6
  • C 3, -7
  • D -3, -7
waec 2016mathematics

The correct answer is C. 3, -7

\(\frac{y^2 - 9y + 18}{y^2 + 4y - 21}\)

Factorize the denominator;

Y2 + 7y - 3y - 21

= y(y + 7) -3 (y + 7)

= (y - 3)(y + 7)

Hence the expression \(\frac{y^2 - 9y + 18}{y^2 + 4y - 21}\) is undefined

when y2 + 4y - 21 = 0

ie. y = 3 or -7

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