Question

So sánh  \(D=\frac{3}{8^3}+\frac{7}{8^4}\)và \(C=\frac{3}{8^4}+\frac{7}{8^3}\)

 

Answer 1

OK

\(D=\frac{3}{8^3}+\frac{7}{8^4}=\frac{3.8}{8^4}+\frac{7}{8^4}=\frac{24+7}{8^4}=\frac{31}{8^4}\)

\(C=\frac{3}{8^4}+\frac{7}{8^3}=\frac{3}{8^4}+\frac{56}{8^4}=\frac{59}{8^4}\)

Mà 59>31 => D<C

Answer 2

\(D=\frac{3}{8^3}+\frac{7}{8^{\text{4}}}=\frac{3}{8^3}+\left(\frac{4}{8^4}+\frac{3}{8^4}\right)\\ \)

\(C=\frac{3}{8^4}+\frac{7}{8^3}=\frac{3}{8^4}+\frac{3}{8^3}+\frac{4}{8^3}\)

vì \(\frac{3}{8^3}+\frac{3}{8^4}+\frac{4}{8^4}>\frac{3}{8^4}+\frac{3}{8^3}+\frac{4}{8^3}\\ =>D>C\)