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\(D=\left(\frac{3}{7}\right)^{21}:\left(\left(\frac{3}{7}\right)^2\right)^6=\left(\frac{3}{7}\right)^{21}:\left(\frac{3}{7}\right)^{2.6}=\left(\frac{3}{7}\right)^9\)
\(E=\left(-\frac{1}{3}\right)^{7+9}:\left(-\frac{1}{3}\right)^{5.3}+\left(-2\right)^{12+3}:\left(-2\right)^{15}=\left(-\frac{1}{3}\right)^{16}:\left(-\frac{1}{3}\right)^{15}+\left(-2\right)^{15}:\left(-2\right)^{15}=-\frac{1}{3}+1=\frac{2}{3}\)
385.22 = 22 + 42 + 62 + ... +202 => 122+ 142 +... + 202 =385.4 - (22+42+ ... + 102)
=> S= 385.4- (22+42+...+102)- (12+32 +...102) = 385.4- (12+22 + +102) - 102 = 385.4- 385 -100= 1055
\(B=x^{15}-8x^{14}+8x^{13}-8x^{12}+...+8x-5\)
\(=x^{15}-\left(x+1\right)x^{14}+\left(x+1\right)x^{13}-\left(x+1\right)x^{12}+...+\left(x+1\right)x-x+2\)
\(=x^{15}-x^{15}-x^{14}+x^{14}+x^{13}-x^{13}-x^{12}+...+x^2+x-x+2\)
\(=2\)
\(A=\frac{2^{12}.27^3}{6^7.16^2}=\frac{2^{12}.3^9}{3^7.2^{15}}=\frac{3^2}{2^3}=\frac{9}{8}\)
\(A=\frac{2^{12}.27^3}{6^7.16}=\frac{2^{12}.3^9}{3^7.2^{15}}=\frac{3^2}{2^3}=\frac{9}{8}\)
~Hok tốt~