square root of -1

Nov 2008
119
47
Here is the mcq:

\(\displaystyle \sqrt{-1}*\sqrt{-1}\)=

a) -1

b) 1 [\(\displaystyle \sqrt{-1*-1}\)]

c) both of a & b

Thanks in advance
 
Feb 2010
60
12
Here is the mcq:

\(\displaystyle \sqrt{-1}*\sqrt{-1}\)=

a) -1

b) 1 [\(\displaystyle \sqrt{-1*-1}\)]

c) both of a & b

Thanks in advance
I would say a) \(\displaystyle -1 \). I was always taught that when multiplying two square roots together, the answer is what ever is under the square root sign i.e. \(\displaystyle \sqrt{2}*\sqrt{2} = 2 \)
 

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MHF Hall of Honor
Mar 2010
2,340
821
Chicago
Using imaginary numbers,

\(\displaystyle \sqrt{-1}\cdot\sqrt{-1}=i\cdot i=-1\).
 
Dec 2007
3,184
558
Ottawa, Canada
TRY the darn thing on something easy; like:
sqrt(4) * sqrt(4)
= 2 * 2
= 4
Kapish?
 

masters

MHF Helper
Jan 2008
2,550
1,187
Big Stone Gap, Virginia
And...

\(\displaystyle \sqrt{-1} \cdot \sqrt{-1}=(-1)^{\frac{1}{2}} \cdot (-1)^{\frac{1}{2}}=(-1)^{\frac{1}{2}+\frac{1}{2}}=(-1)^1=-1\)
 
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