80 bằng 2 mũ mấy ạ
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\(A=\left(5+5^2\right)+\left(5^3+5^4\right)+...+\left(5^{79}+5^{80}\right)\)
\(=30+5^2\left(5+5^2\right)+...+5^{78}\left(5+5^2\right)\)
\(=30\left(1+5^2+...+5^{78}\right)⋮30\)
\(=\left(2^{78}+2^{78}.2+2^{78}.4\right):\left(2^{75}.4+2^{75}.2+2^{75}\right)\)
\(=\left[2^{78}.\left(1+2+4\right)\right]:\left[2^{75}\left(1+2+4\right)\right]\)
\(=\frac{2^{78}.\left(1+2+4\right)}{2^{75}.\left(1+2+4\right)}\)
\(=2^3=8\)
\(=\dfrac{2^{80}\left(1+2+2^2\right)}{2^{78}\left(1+2+2^2\right)}=2^2=4\)
\(293-2^3\cdot3^3+x\div25=80\)
\(293-8\cdot27+x\div25=80\)
\(293-\left(8\cdot27-x\div25\right)=80\)
\(8\cdot27-x\div25=293-80\)
\(216-x\div25=213\)
\(x\div25=216-213\)
\(x\div25=3\)
\(x=3\cdot25=75\)
Vậy x = 3
\(\left(\frac{15}{7}\right)^2+\left(\frac{20}{7}\right)^2=\frac{225}{49}+\frac{400}{49}=\frac{625}{49}\)
\(80=2^4\times5\)
80=2^4 x 5