a, \(\left(\dfrac{12}{25}\right)^x=\left(\dfrac{3}{5}\right)^2-\left(-\dfrac{3}{5}\right)^4\)
\(\Rightarrow\left(\dfrac{12}{25}\right)^x=\left(\dfrac{3}{5}\right)^2.\left[1-\left(\dfrac{3}{5}\right)^2\right]\)
\(\Rightarrow\left(\dfrac{12}{25}\right)^x=\dfrac{9}{25}.\dfrac{16}{25}\Rightarrow\left(\dfrac{12}{25}\right)^x=\dfrac{144}{625}=\left(\dfrac{12}{25}\right)^2\)
Vì \(\dfrac{12}{25}\ne-1;\dfrac{12}{25}\ne0;\dfrac{12}{25}\ne1\) nên \(x=2\)
b, Sửa đề:
\(\left(-\dfrac{3}{4}\right)^{3x-1}=\dfrac{81}{256}\)
\(\Rightarrow\left(-\dfrac{3}{4}\right)^{3x-1}=\left(-\dfrac{3}{4}\right)^4\)
Vì \(\dfrac{-3}{4}\ne-1;\dfrac{-3}{4}\ne0;\dfrac{-3}{4}\ne1\) nên \(3x-1=4\)
\(\Rightarrow3x=5\Rightarrow x=\dfrac{5}{3}\)
Vậy......
Chúc bạn học tốt!!!
Hồng Phúc Nguyễn, Hà Linh, Trương Hồng Hạnh, Hoàng Ngọc Anh, @Nguyễn Thanh Hằng, @Nguyễn Đinh Huyền Mai, ...
