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15 Apr 2018, 10:00
Kudos
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C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
5%
(low)
Question Stats:
99% (00:44) correct
1%
(00:28)
wrong
based on 147
sessions
History
Date
Time
Result
Not Attempted Yet
15 Apr 2018, 10:30
Kudos
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Bunuel
We'll show two approaches.
The Precise approach involves straight up calculation:
9^2 - 2*9 + 1 = 81 - 18 + 1 = 64, the square root of which is 8.
Note that the 'square root function' always returns a positive number which is why (A) is incorrect.
(C) is our answer.
We could also have estimated the answer, an Alternative approach.
We know that the square root of x^2 is x. Since we're asked for the square root of something smaller than x^2 (e.g. x^2 - 2*x+1) we know the answer must be smaller than x.
Only C and B make sense but we can estimate (without calculating) that (B) is too far: 5^2 = 25 and 81 - 18 + 1 is about 60, much larger than that.
Note that in this case estimation is not necessary as the equation is simple, however it can be very useful for difficult calculations.
