\( \mathrm{C}=\frac{\sqrt{3}}{\sqrt{3}+1}-\frac{\sqrt{3}-1}{\sqrt{3}+2}- \) et \( D=\left(\sqrt{5}+\frac{1}{\sqrt{5}}\right)^{2} \) 3) Soient \( x, y \) et \( z \) trois nombres réels strictement positifs. a) Montre que si \( x y+y z+x z=0 \) alors \( \frac{y+z}{x}+\frac{x+z}{y}+\frac{x+y}{z}=-3 \).

6) \( \frac{3 a^{-2}-4 b^{-1}+a b}{3 a b-2 a} \quad a=3 ; b=4 \)

Without actually calculating, find the value \( (-10)^{3}+(7)^{3}+(3)^{3} \) వాస్తవ గణన చేయకుండానే \( (-10)^{3}+(7)^{3}+(3)^{3} \) యొక్క విలువ కనుక్కోఁ

4. Math on the Spot Solve each system by substitution. \( \begin{array}{ll}\text { A. }\left\{\begin{array}{l}y=3 x \\ y=x+4\end{array}\right. & \text { B. }\left\{\begin{array}{l}x-y=4 \\ x+2 y=4\end{array}\right.\end{array} \)

4. \( \frac{(4 n)!+(4 n+1)!}{(4 n+1)!-(4 n)!} \) ifadesinin eşiti aşağıdakilerden han- gisidir? \( \begin{array}{ll}\text { A) } \frac{2 n+1}{2} & \text { B) } \frac{2 n+1}{n} \\ \text { C) } \frac{2 n+1}{2 n} & \text { D) } \frac{2 n}{2 n+1}\end{array} \)

A straight highway connects Town A and Town B, a distance of 45 kilometres, Andy started biking along the highway from Town A to Town B at 8:00 AM at a constant speed of 3 kilometres per hour. Ben started biking on a parallel highway from Town B to Town A at 9:00 AM at a constant speed of 4 kilometres per hour. How many kilometres had Ben biked when they met along the way?