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Which of the following is a solution of x 2 + 2x – 8 = 7?
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19 Jul 2019, 08:18
19 Jul 2019, 08:18
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Which of the following is a solution of \(x^2 + 2x – 8 = 7\)?
(A) 4
(B) –3
(C) 2
(D) 3
(E) 5
(A) 4
(B) –3
(C) 2
(D) 3
(E) 5
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Re: Which of the following is a solution of x 2 + 2x – 8 = 7?
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19 Jul 2019, 08:47
19 Jul 2019, 08:47
Carcass wrote:
Which of the following is a solution of \(x^2 + 2x – 8 = 7\)?
(A) 4
(B) –3
(C) 2
(D) 3
(E) 5
(A) 4
(B) –3
(C) 2
(D) 3
(E) 5
One approach is to test each answer choice.
I'll leave it to students to do that.
Another (and likely faster) approach is the factor the quadratic (once we have set the quadratic equal to zero)
Take: \(x^2 + 2x – 8 = 7\)
Subtract 7 from both sides of the equation to get: \(x^2 + 2x – 15 = 0\)
Factor to get: \((x-3)(x+5)=0\)
So EITHER \((x-3)=0\) OR \((x+5)=0\)
If \((x-3)=0\), then \(x=3\)
Check the answer choices...
BINGO!
Answer: D
Cheers,
Brent
Which of the following is a solution of x 2 + 2x 8 = 7?
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09 Jun 2023, 20:52
09 Jun 2023, 20:52
Which of the following is a solution of \(x^2+2x–8=7\) ?
Lets rewrite the equation in the standard form as
\(x^2 + 2x - 8 - 7 = 0\)
\(x^2 + 2x - 15 = 0\)
Now, we need to think of two numbers that multiply to \(-15\) and add to \(+ 2\).
They are definitely \(5\) and \(-3\)
Now, just flip their signs -> \(-5\) and \(3\) to get the solutions to the equations!
And since only \(3\) is in the choices, Choice D is the answer! Bingo!
Lets rewrite the equation in the standard form as
\(x^2 + 2x - 8 - 7 = 0\)
\(x^2 + 2x - 15 = 0\)
Now, we need to think of two numbers that multiply to \(-15\) and add to \(+ 2\).
They are definitely \(5\) and \(-3\)
Now, just flip their signs -> \(-5\) and \(3\) to get the solutions to the equations!
And since only \(3\) is in the choices, Choice D is the answer! Bingo!
