Simplify. \[ \frac{20 a^{-9} b^{-2} c^{7}}{4 b^{5} c^{-4}} \] Write your answer using only positive exponents.

268. Решите уравнение: \( \begin{array}{l}\text { а) }(y+2)\left(y^{2}-2 y+4\right)-y(y-3)(y+3)=44 \text {; } \\ \text { б) }(m-3)\left(m^{2}+3 m+9\right)-m(m+2)(m-2)=13 \text {; } \\ \text { B) }(3 a+1)\left(9 a^{2}-3 a+1\right)-3 a\left(9 a^{2}+4\right)=25 \text {; }(2 n-1)\left(4 n^{2}+2 n+1\right)-4 n\left(2 n^{2}-5\right)=21 \text {. }\end{array} \).

7. \( a, b \) ve \( c \) gerçel sayıları için \( a>0>b \cdot a \) \( b>c \) olduğuna göre, aşağıdakilerden hangisi kesinlil pozitiftir? \( \begin{array}{lll}\text { A) } a \cdot c & \text { B) } a \cdot b \cdot c & \text { C) } c \\ \text { D) } a+c & \text { E) } b^{2} \cdot c\end{array} \)

Evaluate the following function. Your answer should be an integer. \( f(x)=-3^{2 x-2} \), for \( x=3 \) Your answer is \( f(3)=\square \)

268. Решите уравнение: \( \begin{array}{l}\text { а) }(y+2)\left(y^{2}-2 y+4\right)-y(y-3)(y+3)=44 \text {; } \\ \text { б) }(m-3)\left(m^{2}+3 m+9\right)-m(m+2)(m-2)=13 \text {; } \\ \text { (B) }(3 a+1)\left(9 a^{2}-3 a+1\right)-3 a\left(9 a^{2}+4\right)=25 \text {; } \\ \text { (A) }(2 n-1)\left(4 n^{2}+2 n+1\right)-4 n\left(2 n^{2}-5\right)=21 \text {. }\end{array} \)

\( \sqrt { n ^ { 2 } - 1 } - ( n + 1 ) = \frac { ( n ^ { 2 } - 1 ) - ( n + 1 ) ^ { 2 } } { \sqrt { n ^ { 2 } - 1 } + ( n + 1 ) } = \frac { - 2 n - 2 } { \sqrt { n ^ { 2 } - 1 } + ( n + 1 ) } \rightarrow - 1 \)