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Now I was doing some physics and I got to this equation, task is solved but i don't get this part... So is it possible to get for

$$\frac{m_1(v^2_1-w_1^2)}{m_1(v_1+w_1)}=w_2$$ to $v_1-w_1=w_2$.

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$$\frac{m_1 (v_1^2 - w_1^2)}{m_1 (v_1 + w_1)} = \frac{m_1 (v_1 - w_1)(v_1 + w_1)}{m_1 (v_1 + w_1)} = v_1 - w_1$$

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that was really fast :) – Ragnar Feb 20 '14 at 22:43
@Ragnar: The difference of squares shows up often. It is useful to recognize its factorization. – Ross Millikan Feb 20 '14 at 22:45
oh of course, thank you – Psiatronium Feb 20 '14 at 22:54
@RossMillikan, I know how to solve it, but to write it down within a minute from asking is fast. – Ragnar Feb 21 '14 at 1:24

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