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# Square roots

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Hi good people!, for the following sum I get a different answer to the book, and no matter how many times I do this sum, I keep getting the same answer. please help me to see where I'm going wrong?

$$\sqrt{-5}(\sqrt{-3} * \sqrt{-4})$$

$$\sqrt{5*-1}(\sqrt{3*-1}* \sqrt{2^2 *-1})$$

$$\sqrt{5i}(\sqrt{3i}* \sqrt{2^2i})$$

$$\sqrt{5i}(\sqrt{3i}* 2 \sqrt{i})$$

$$\sqrt{15i^2}*2(-1)$$$$​​​​$$$$​​​​$$

$$-2 \sqrt{15i^2}$$

The book says $$-2 \sqrt{15i}$$

Thanx for the help!!

Jan 22, 2019

#1
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Hi Juriemagic :)

$$\sqrt{-5}=\sqrt{5*-1}=\sqrt5*\sqrt{-1}=\sqrt5\;i$$

So your mistakes strat in the third row.

$$\sqrt{-5}(\sqrt{-3}*\sqrt{-4})\\ \sqrt5*\sqrt3*\sqrt4*i*i*i\\ 2\sqrt{15}*-1*i\\ -2\sqrt{15}\;i$$

Are you sure you copied in the book answer correctly?

Jan 22, 2019
#4
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Hello Melody!!!!,

I am going to be VERY honest about this....the answer I actually got, was exactly the same as what you got...I promise you that. this morning when I posted the problem, i did not have my paper that i worked on, with me, so I did the sum afresh...and got lost. I figured that it was'nt a train smash if i did not put the sum exactly as I actually had it....the answer is wrong any case...so I left it as such

Yes I also did the 3 "i"'s etc...

Melody, yes, I checked and re-checked that answer....the "i" looks like it is within the square root sign...maybe they did a mis-print?

juriemagic  Jan 22, 2019
#5
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Yes it would have been a misprint.  :)

or a poor print  ;)

Melody  Jan 22, 2019
edited by Melody  Jan 22, 2019
#6
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Melody,

Thank you very much for your assistance...appreciated!!

juriemagic  Jan 22, 2019
#7
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It is always a pleasure to help you Juriemagic Melody  Jan 22, 2019