8) (B. 1 ball.) Birhadni ko'phadga ko paytiring: \( 3 x^{2} y(5 x-6 y+7 z) \) \( \begin{array}{ll}\text { A) } 15 x^{3} y-18 x^{2} y^{2}-21 x^{2} y z & \text { B) } 15 x^{3} y+18 x^{2} y^{2}+21 x^{2} y z \\ \text { C) } 15 x^{3} y-18 x^{2} y^{2}+21 x^{2} y z & \text { D) } 15 x^{3} y+18 x^{2} y^{2}-21 x^{2} y z\end{array} \)

Il rapporto tra la differenza di due numeri e la somma aumentata di 6 è \( \frac{1}{3} \). Aggiungendo 3 al numero minore e togliendo 6 al maggiore, si ottie- ne lo stesso risultato. Determina i due numeri. \( [6 ; 15] \)

49. \( 12 a b x^{2}-9 a^{2} x+8 b^{2} x-6 a b=0 \Rightarrow \)

5. Simplify the following expressions and find the value when \( x=-2 \).

When \( a=-1, b=0 \), find the value of: \( \begin{array}{ll}\text { (i) } 2 a+3 b & \text { (ii) } 4 a^{2} b+a b^{2}+a b\end{array} \)

\begin{tabular}{l} 3. \\ Derive an algebraic expression for \( S_{n} \). \\ INSTRUCTION: Simplify your answer \\ completely. \\ Answer: \\ \( S_{n}= \) \\ \hline Check answer 2 attempts remaining \\ \hline Help! How should I type my answer? \\ \hline\end{tabular}