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
Correct Answer: Option 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