Final answer:
The value of 'a' cannot be determined without the actual expression provided. The question references quadratic equations, which involve a different set of variables and operate with the quadratic formula.
Step-by-step explanation:
The question does not provide an expression or enough context to determine the value of a for the equation 1−xa. However, given the general nature of quadratic equations as referenced in the provided information, it's possible the question intends to refer to a standard quadratic equation of the form ax2 + bx + c = 0, where a, b, and c are constants.
In this case, the solution for x would be obtained using the quadratic formula, which is x = −b ± √(b2 − 4ac) / 2a. However, without the specific expression that equals 1−xa, we cannot accurately determine the value of a. Should the student provide the exact expression, a direct calculation could be performed to find the value of a.