12. \( a^{2 n+1}+a^{2} b^{n+1}-b^{2 n-1}-a^{n+2} b \) ifadesinin vuruqlanndan biri aşagıdaklardan hansidn \( \begin{array}{llll}\text { A) } a^{2 n-1}+b^{n+1} & \text { B) } a^{n} & \text { C) } a^{2}+b & \text { D) } a^{2 n-1}-b\end{array} \)

Evaluate \( \left(\frac{3.5^{7}}{3.5^{6}}\right)^{2} \)

(c) Subtract: \( 31(1-4 m+5 n) \) from \( 4 I(10 n-3 m+21) \) (d) Subtract: \( 3 a(a+b+c)-2 b(a-b+c) \) from \( 4 c(-a+b+c \)

\( \frac { 1 } { r } \times \frac { 1 - ( \frac { 1 } { r } ) ^ { n } } { 1 - \frac { 1 } { r } } \geq \frac { 9 r } { 100 } \Rightarrow 1 - \frac { 1 } { r ^ { n } } \geq \frac { 9 r } { 100 } \)

act: \( 3 I(I-4 m+5 n) \) from \( 4 I(10 n-3 m+2 l) \) act: \( 3 a(a+b+c)-2 b(a-b+c) \) from \( 4 c(-a+b+c) \)

3. ( 0,5 điểm) Tìm \( x \) biết: \( x^{2}(x-1)+4=4 x \)