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 h
1 answer:
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: , 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
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Answer:
Quadratic Formula
so
x = -5
and
x = 0.5
Step-by-step explanation:
Whenever you see a problem in this form, which you will see a lot of, you can try to factor it or use the "least squares" method or what have you, but those won't always work, unfortunately.
Fortunately, the quadratic formula will never fail you with quadratic expressions.
This is the Quadratic Formula
a is the the number on the variable with the exponent ^2
b is the number on the variable with no exponent
c is the third number
a and b cannot be equal to 0; c can be
Since we're looking for a number with an equation that has a square root in it, we're going to get two answers. These two answers come from the radical being separately added AND subtracted from the radical. It's basically two problems.
Plugging in our numbers to this equation gives us x values of -5 and 0.5. This will always work with polynomials with factors of ^2 in them.
If you have a TI-84 calculator or newer, there's a tool on it that will factor polynomials like this one for you just by giving it the numbers.