Question

[Nguyễn Bạch Trường Giang]

1. Tìm x:

 \(\left(\frac{4}{5}\right)^{2x+7}=\frac{625}{256}\)

2. So sánh:

\(a=15^{120}:25^{60}\)và \(b=2^{45}.2^{15}.4^{60}\)

Answer 1

[Phan Văn Hiếu]

\(a=\left(15^2\right)^{60}:25^{60}\)

\(a=225^{60}:25^{60}\)

\(a=\left(225:25\right)^{60}=9^{60}\)

\(b=2^{45}.2^{15}.2^{120}\)

\(b=2^{180}=8^{60}\)

vì \(8^{60}< 9^{60}\)nên b<a

Answer 2

[Phan Văn Hiếu]

1,\(\left(\frac{4}{5}\right)^{2x+7}=\left(\frac{4}{5}\right)^{-4}\)

\(\Rightarrow\)2x+7=-4

2x=-11

x=-5,5