The equation x2 – 1x – 90 = 0 has solutions {a, b}. What is a + b?

For a quadratic equation ax² + bx + c = 0, the sum of the solutions is −b/a. Here, x² − x − 90 = 0, so a = 1 and b = −1. Thus the sum is −(−1)/1 = 1, which is choice C.

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