Answer:
3.69 (rounded)
Step-by-step explanation:
Substitute x for "a number".
New equation: x(x + 2) = 21
Distribute and combine to form a single equation: x^2 + 2x - 21 = 0
Use quadratic formula, factoring, or graphing to get all possible answers.
Quadratic formula: [tex]x=(-b\frac{+}{} \sqrt{b^{2}-4ac }) \frac{1}{2a}[/tex], where A = x^2 coefficient, B = x coefficient, and C = constant.
-5.69, 3.69
Eliminate an incorrect answer that does not line up with the above equation.
3.69
