Toán Lớp 7: B=3+3 mũ 2 + 3 mũ 3 +…….+3 mũ 50 đề bài rút gọn
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Toán Lớp 7: B=3+3 mũ 2 + 3 mũ 3 +…….+3 mũ 50 đề bài rút gọn
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Comments ( 2 )
B = 3 + {3^2} + {3^3} + … + {3^{50}}\\
\Leftrightarrow 3.B = {3^2} + {3^3} + {3^4} + … + {3^{51}}\\
\Leftrightarrow 3B – B = {3^{51}} – 3\\
\Leftrightarrow 2B = {3^{51}} – 3\\
\Leftrightarrow B = \dfrac{{{3^{51}} – 3}}{2}
\end{array}$