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sorry if this seems to be too easy for you, but I have struggled a lot with this expression and I don't get it how they got there:

enter image description here

How can $\sqrt{2x^2}$ become $4x^2$ ?

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    $\begingroup$ Mathoverflow is for research level math questions. Try math.stackexchange. $\endgroup$ – JoshuaZ Sep 25 '19 at 15:53
  • $\begingroup$ ah I see, ok. I will post on the other platform from now on. $\endgroup$ – artgrohe Sep 26 '19 at 8:25
  • $\begingroup$ you can delete this answer if you want, since it's off-topic. I cannot delete it.. $\endgroup$ – artgrohe Sep 26 '19 at 8:53
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You need to multiply the numerator and the denominator by $2 \sqrt{2x^2}$ to obtain the second equation from the first.

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  • $\begingroup$ thanks! how could I not see this... $\endgroup$ – artgrohe Sep 26 '19 at 8:27

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