122k views
3 votes
Write as a mathematical expression and solve. The sum of a number and 2 times the number is 21. Find the number. i really need help please help

User Reveille
by
8.6k points

1 Answer

2 votes

Answer:

3.69 (rounded)

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:
x=(-b\frac{+}{} \sqrt{b^(2)-4ac }) (1)/(2a), 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

User Tendayi Mawushe
by
7.5k points

No related questions found

Welcome to QAmmunity.org, where you can ask questions and receive answers from other members of our community.

9.4m questions

12.2m answers

Categories