Find the values of y for which the expression \(\frac{y^2 – 9y + 18}{y^2 + 4y – 21}\) is undefined
- 6, -7
- 3, -6
-
3, -7
- -3, -7
The correct answer is: C
Explanation
\(\frac{y^2 - 9y + 18}{y^2 + 4y - 21}\)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