MCQ
If $\left|\begin{array}{cc}x & 2 \\ 15 & x\end{array}\right|=\left|\begin{array}{ll}6 & 6 \\ 3 & 4\end{array}\right|$ then $x=$ _________.
- A$- 6$
- B6
- C$\pm 6$
- D$0$
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$(a+b)-\left(\frac{a^{2}+b^{2}}{2}\right)+\left(\frac{a^{3}+b^{3}}{3}\right)-\left(\frac{a^{4}+b^{4}}{4}\right)+\ldots$ is ..... .