7.滿足聯立方程組cases x - 2y + z = 7 \ 3x + y - 2z = -1 \ 2x - 3y + z = 10 cases的x值為何？(A)2(B)4(C)6(D)8

12.設\( f(x) = 3^x \), \( g(x) = \log_{\frac{1}{3}} x \)，則下列選項何者正確？(A)若x1<x2，則\( 3^{x_1} > 3^{x_2} \)(B)若x1<x2，則\( 3^{x_1} + 3^{x_2} = 3^{x_1+x_2} \)(C)若x1<x2，則\( \log_{\frac{1}{3}}(x_2 - x_1) = \log_{\frac{1}{3}} x_2 - \log_{\frac{1}{3}} x_1 \)(D)若x1<x2，則\( \frac{\log_{\frac{1}{3}} x_2 - \log_{\frac{1}{3}} x_1}{x_2 - x_1} < 0 \)