Question

Mathieu is finding the x-intercepts of the function
f(x) = x2 + 4x + 3. His work is shown below.

0 = x2 + 4x + 3
0 = (x + 3)(x + 1)
x + 3 = x + 1
x = x – 2
0 = –2
There are no x-intercepts.
Which error did Mathieu make?

He factored incorrectly.
He did not use the constant as the x-intercept.
He set the factored expressions equal to each other.
He incorrectly solved the equation x + 3 = x + 1.

Answer 1

He set the factored expressions equal to each other.

From (x + 3)(x + 1) = 0 you must set each factor equal to 0: x + 3 = 0 or x + 1 = 0, giving x = -3 and x = -1.