\begin{tabular}{l} Mengapa lemak dianggap sebagai \\ sumber energi yang efisien bagi \\ tubuh? \\ A. Lemak mengandung lebih banyak \\ kalori per gram dibandingkan \\ karbohidrat dan protein \\ B. Lemak mudah disimpan dan \\ dibakar di dalam tubuh \\ \( \begin{array}{l}\text { C. Lemak tidak memerlukan proses } \\ \text { pencernaan }\end{array} \) \\ \( \begin{array}{l}\text { D. Lemak langsung diubah menjadi } \\ \text { energi tanpa proses metabolisme }\end{array} \) \\ \hline\end{tabular}

a) \( (x+1) y^{\prime \prime}+x y^{\prime}-y=(x+1)^{2} \) b) \( x^{2} y^{\prime \prime}-3 x y^{\prime}+4 y=x^{2} \) (bonus, +1.5 p ) Solve the DE

\[ -\quad-x_{1}+2 x_{2}-7 x_{3}=4 \] 3. (30 points) Solve the system of linear equations using Gauss-Jordan method. Find the rank of the matrix of this system. Indicate dependent and independent variables. Find the fundamental solution set (write the answer as a linear combination of particular vectors) \[ \begin{array}{l}x_{1}+3 x_{2}+2 x_{3}-3 x_{4}=0 \\ 2 x_{1}+6 x_{2}+3 x_{3}-4 x_{4}=0 \\ 3 x_{1}+9 x_{2}+4 x_{3}-5 x_{4}=0\end{array} \]

b) \( x^{2} y^{\prime \prime}-3 x y^{\prime}+4 y=x^{2} \) (bonus, +1.5 p ) Solve the DE

a) \( x^{2}+5 x+1 \)

\( y=\log _{2} x \), the \( y \)-axis, \( y=0 \) and \( y=2 \)