Question

Error Analysis A student evaluated - 4 + x for x = - 9 and got an answer of 5. What might the student have done wrong?

Analyzing functions
Error Analysis A student evaluated $$- 4 + x\ for\ x = - 9$$ and got an answer of 5. What might the student have done wrong?
He might have substituted $$x=9$$, because it is easy to check that $$-4+9=5$$