Помогите решить задание 4,вариант 1

A) $7^{3-x}\ \textless \ \frac{1}{49} \\ 7^{3-x}\ \textless \ 7^{-2} \\ 3-x\ \textless \ -2 \\ -x\ \textless \ -2-3 \\ -x\ \textless \ -5 \\ x\ \textgreater \ 5$
x∈(5; +∞)
Ответ: (5; +∞)

б) $(\frac{1}{3})^{x^2-4x-1}\ \textgreater \ 9^{x-1} \\ (3^{-1})^{x^2-4x-1}\ \textgreater \ (3^2)^{x-1} \\ -x^2+4x+1\ \textgreater \ 2x-2 \\ -x^2+4x-2x+1+2\ \textgreater \ 0 \\ x^2-2x-3\ \textless \ 0 \\ x^2-2x-3=0 \\ D=4+12=16 \\ x_{1}= \frac{2-4}{2}=-1 \\ x_{2}= \frac{2+4}{2}=3 \\$
+ - +
--------- -1 --------- 3 ------------
\\\\\\\\\\\
x∈(-1; 3)
Ответ: (-1; 3)

в) $3^{x}-3^{x-3}\ \textgreater \ 26 \\ 3^{x}- \frac{3^{x}}{3^3}\ \textgreater \ 26 \\ 3^{x}(1- \frac{1}{27} )\ \textgreater \ 26 \\ 3^{x}* \frac{26}{27}\ \textgreater \ 26 \\ 3^{x}\ \textgreater \ 26* \frac{27}{26} \\ 3^{x}\ \textgreater \ 27 \\ 3^{x}\ \textgreater \ 3^3 \\ x\ \textgreater \ 3$
x∈(3; +∞)
Ответ: (3; +∞)