Two soap bubbles coalescing isothermally

1. A.
   $R=\frac{r_1+r_2}{2}$
2. B.
   $R=\frac{r_1 r_1}{r_2+r_2}$
3. C.
   $R=\sqrt{r_1^2+r_2^2}$
4. D.
   $R=r_1+r_2$

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1. A.
   $a+b$
2. B.
   $\frac{a+b}{2}$
3. C.
   $\sqrt{a^2+b^2}$
4. D.
   $\frac{a+b}{ab}$

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1. A.
   $\left( r_{1} + r_{2} \right)^{\frac{1}{2}}$
2. B.
   $\left( r_{1} + r_{2} \right)^{2}$
3. C.
   $\left( r_{1}^{2} + r_{2}^{2} \right)^{\frac{1}{2}}$
4. D.
   $\left( r_{1} + r_{2} \right)^{3}$

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1. A.
   $\dfrac{P(R^3 - r_1^3 - r_2^3)}{4(r_1^2 + r_2^2 - R^2)}$
2. B.
   $\dfrac{P(R^3 + r_1^3 + r_2^3)}{2(r_1^2 - r_2^2 + R^2)}$
3. C.
   $\dfrac{P(r_1^3 - r_2^3 - R^3)}{(R^2 + r^2 + r^2)}$
4. D.
   $\dfrac{P(R^3 - r_1^3 + r_2^3)}{2(r_1^2 + r_2^2 - R^2)}$

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