(3) If the point \( (x-5,7-x) \) lies in the second quadrant, then \( x=- \) \( \begin{array}{lll}\text { (a) } 9 & \text { (b) } 3 & \text { (c) } 7\end{array} \)

Exercise 3.17 Determine if each one of the following system of linear equations has unique solution, no solution or infinitely many solutions. \( \begin{array}{ccc}x-y=1 & \text { b. } \begin{array}{c}x+y=1 \\ 2 x+3 y=4\end{array} & \begin{array}{c}x-2 y=1 \\ x+y=5\end{array} \\ \begin{array}{l}\text { a. } \\ x+4 y=2\end{array}\end{array} \)

Si \( a = 4 \), ¿cuál es el valor de \( a^2 \)?

b. प्रमाणित गर्नुहोस् (Prove that): \( \frac{1}{1-\mathrm{x}^{\mathrm{a}-\mathrm{b}}}+\frac{1}{1-\mathrm{x}^{\mathrm{b}-\mathrm{a}}}=1 \)

Solve the exponential equation: \( 3^{2x} = 81 \)

a \( \frac{x^{3}-3 x^{2}+5}{x^{2}} \)