If x = 3 is one solution to the equation x² + rx - 20 = 4, then r = ___?
- 5
- -5
- -8
- None of these
Explanation
Given that x = 3 is a solution to the equation:
x² + rx - 20 = 4
Substitute x = 3 into the equation:
(3)² + r(3) - 20 = 4
Simplify:
9 + 3r - 20 = 4
Combine like terms:
3r - 11 = 4
Add 11 to both sides:
3r = 15
Divide by 3:
r = 5
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