x² - 2x - 3 = 0Which of the following expressions CANNOT be equal to 0 when x² − 2x = 3?
A. x² − 6x + 9
B. x² − 4x + 3
C. x² − x − 2
D. x² − 7x + 6
E. x² − 9
(x-3)(x+1) = 0
x=3 or x=-1.
Eliminate any answer choice that CAN be equal to 0 when x=3 or x=-1.
A wise test-taker knows the following:
When the question stem includes the phrase which of the following, the correct answer is likely to be D or E.
E: x² − 9
If we plug x=3 into x² − 9, we get:
3² − 9 = 0.
Eliminate E.
D: x² − 7x + 6
If we plug x=3 into x² − 7x + 6, we get:
3² − 7*3 + 6 = -6.
If we plug x=-1 into x² − 7x + 6, we get:
(-1)² − 7(-1) + 6 = 14.
x² − 7x + 6 cannot be equal to 0 when x=3 or x=-1.
The correct answer is D.
