# Thread: square root of -1

1. ## square root of -1

Here is the mcq:

$\sqrt{-1}*\sqrt{-1}$=

a) -1

b) 1 [ $\sqrt{-1*-1}$]

c) both of a & b

2. Originally Posted by u2_wa
Here is the mcq:

$\sqrt{-1}*\sqrt{-1}$=

a) -1

b) 1 [ $\sqrt{-1*-1}$]

c) both of a & b

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

3. Using imaginary numbers,

$\sqrt{-1}\cdot\sqrt{-1}=i\cdot i=-1$.

4. TRY the darn thing on something easy; like:
sqrt(4) * sqrt(4)
= 2 * 2
= 4
Kapish?

5. Originally Posted by Wilmer
TRY the darn thing on something easy; like:
sqrt(4) * sqrt(4)
= 2 * 2
= 4
Kapish?
Everything except kapish...

6. And...

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