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Which of the following equals
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09 Aug 2017, 15:23
09 Aug 2017, 15:23
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88% (01:10) correct
11% (02:07) wrong based on 179 sessions
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Which of the following equals \(- ( \sqrt{2} - \sqrt{8} ) ( 2 \sqrt{2} + \sqrt{8} )\) ?
A. \(-8 \sqrt{2}\)
B. -4
C. 4
D. \(4 \sqrt{2}\)
E. 8
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Re: Which of the following equals
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12 Aug 2017, 06:03
12 Aug 2017, 06:03
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Carcass wrote:
Which of the following equals \(- ( \sqrt{2} - \sqrt{8} ) ( 2 \sqrt{2} + \sqrt{8} )\) ?
A. \(-8 \sqrt{2}\)
B. -4
C. 4
D. \(4 \sqrt{2}\)
E. 8
A. \(-8 \sqrt{2}\)
B. -4
C. 4
D. \(4 \sqrt{2}\)
E. 8
Let's apply the FOIL method.
We'll also use the fact that (√a)(√b) = √(ab)
So, -(√2 - √8)(2√2 + √8) = -(2√4 + √16 - 2√16 - √64)
= -(4 + 4 - 8 - 8)
= -(-8)
= 8
Answer: E
Re: Which of the following equals
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04 May 2020, 03:15
04 May 2020, 03:15
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A shortcut to this is to consider root(2) instead of 2root(2) in the second bracket. Using a^2 - b^2 = (a+b)(a-b) formula, we get -[2-8] = -(-6) = 6
Now when we multiply 2 numbers, A * B, if B increases, then the total product increases too.
The initial product value is 6, but we add one more root(2) to B, so the total product value should be more than 6. The minus sign outside the product in the question makes it invariably positive.
The only option greater than 6 is 8. (E)
Now when we multiply 2 numbers, A * B, if B increases, then the total product increases too.
The initial product value is 6, but we add one more root(2) to B, so the total product value should be more than 6. The minus sign outside the product in the question makes it invariably positive.
The only option greater than 6 is 8. (E)
