5.$\int_{{}}^{{}}{\frac{\cos 2x}{1+\sin x\cos x}dx}=$()。
A. $\ln |1+\sin x\cos x|+C$
B. $\ln |\sin x\cos x|+C$
C. $\ln |1-\sin x\cos x|+C$
D. $\frac{-1}{1+\sin x\cos x{{}^{2}}}+C$
4.设$\int_{{}}^{{}}{f(x)dx}={{x}^{2}}+C$,则$\int_{{}}^{{}}{xf(1-{{x}^{2}})dx}=$()。
A. $-2{{(1-{{x}^{2}})}^{2}}+C$
B. $2{{(1-{{x}^{2}})}^{2}}+C$
C. $-\frac{1}{2}{{(1-{{x}^{2}})}^{2}}+C$
D. $\frac{1}{2}{{(1-{{x}^{2}})}^{2}}+C$
3.设$f(x)=\left\{ \begin{array}{*{35}{l}}{{x}^{2}}, x\le 1, \\2-x, x\gt 1 \\ \end{array} \right.$,则下列函数中,为$f(x)$的原函数的是()。
A. $F(x)=\left\{ \begin{array}{*{35}{l}}\frac{{{x}^{3}}}{3}, x\le 1, \\\frac{1}{2}+2x-\frac{{{x}^{2}}}{2}, x\gt 1 \\ \end{array} \right.$
B. $F(x)=\left\{ \begin{array}{*{35}{l}}\frac{{{x}^{3}}}{3}, x\le 1, \\-\frac{7}{6}+2x-\frac{{{x}^{2}}}{2}, x\gt 1 \\ \end{array} \right.$
C. $F(x)=\left\{ \begin{array}{*{35}{l}}\frac{{{x}^{3}}}{3}, x\le 1, \\\frac{1}{2}-2x-\frac{{{x}^{2}}}{2}, x\gt 1 \\ \end{array} \right.$
D. $F(x)=\left\{ \begin{array}{*{35}{l}}\frac{{{x}^{2}}}{3}, x\le 1, \\\frac{7}{6}+2x-\frac{{{x}^{2}}}{2}, x\gt 1 \\ \end{array} \right.$
2.下列函数中,在$(-\infty ,+\infty )$上不存在原函数的是()。
A. $f(x)=|x|$
B. $f(x)=\left\{ \begin{array}{*{35}{l}}\sin x, x\le \frac{\pi }{2}, \\1, x \gt \frac {\pi }{2} \\ \end{array} \right.$
C. $f(x)=\left\{ \begin{array}{*{35}{l}}-1, x\le \frac{\pi }{2}, \\1, x \gt \frac{\pi }{2} \\ \end{array} \right.$
D. $f(x)=\left\{ \begin{array}{*{35}{l}}{{x}^{2}}, x\le 2, \\6-x, x \gt 2 \\ \end{array} \right.$