第1个回答 2017-09-16
∵y<sub>1</sub>(x),y<sub>2</sub>(x),y<sub>3</sub>(x)是二阶非齐次线性微分方程y″+p(x)y′+q(x)y=f(x)的三个线性无关解
∴y<sub>1</sub>(x)-y<sub>2</sub>(x),y<sub>2</sub>(x)-y<sub>3</sub>(x);y<sub>1</sub>(x)-y<sub>3</sub>(x),y<sub>2</sub>(x)-y<sub>3</sub>(x);y<sub>1</sub>(x)-y<sub>2</sub>(x),y<sub>1</sub>(x)-y<sub>3</sub>(x);
是对应齐次的三组两个线性无关的解
∴对应齐次的通解就可以表示成:
①选项A.由于C<sub>1</sub>y<sub>1</sub>(x)+(C<sub>1</sub>-C<sub>2</sub>)y<sub>2</sub>(x)+(1-C<sub>2</sub>)y<sub>3</sub>(x)=C<sub>1</sub>[y<sub>1</sub>(x)+y<sub>2</sub>(x)]-C<sub>2</sub>[y<sub>2</sub>(x)+y<sub>3</sub>(x)]+y<sub>3</sub>(x)
而y<sub>1</sub>(x)+y<sub>2</sub>(x)和y<sub>2</sub>(x)+y<sub>3</sub>(x)都不是齐次的解
故选项A错误.
②选项B.由于(C<sub>1</sub>-C<sub>2</sub>)y<sub>1</sub>(x)+(C<sub>2</sub>-1)y<sub>2</sub>(x)+(1-C<sub>1</sub>)y<sub>3</sub>(x)=C<sub>1</sub>[y<sub>1</sub>(x)-y<sub>3</sub>(x)]-C<sub>2</sub>[y<sub>1</sub>(x)-y<sub>2</sub>(x)]-[y<sub>3</sub>(x)-y<sub>2</sub>(x)]
而y<sub>1</sub>(x)-y<sub>3</sub>(x)、y<sub>1</sub>(x)-y<sub>2</sub>(x)、y<sub>3</sub>(x)-y<sub>2</sub>(x)都是齐次的解,且只有两个任意常数
故选项B正确
③选项C.由于(C<sub>1</sub>+C<sub>2</sub>)y<sub>1</sub>(x)+(C<sub>1</sub>-C<sub>2</sub>)y<sub>2</sub>(x)+(1-C<sub>1</sub>)y<sub>3</sub>(x)=C<sub>1</sub>[y<sub>1</sub>(x)+y<sub>2</sub>(x)-y<sub>3</sub>(x)]+C<sub>2</sub>[y<sub>1</sub>(x)-y<sub>2</sub>(x)]+y<sub>3</sub>(x)
而y<sub>1</sub>(x)+y<sub>2</sub>(x)-y<sub>3</sub>(x)、y<sub>3</sub>(x)都不是齐次的解
故选项C错误.
④选项D.由于C<sub>1</sub>y<sub>1</sub>(x)+C<sub>2</sub>y<sub>2</sub>(x)+(1-C<sub>1</sub>-C<sub>2</sub>)y<sub>3</sub>(x)=C<sub>1</sub>[y<sub>1</sub>(x)-y<sub>3</sub>(x)]+C<sub>2</sub>[y<sub>2</sub>(x)-y<sub>3</sub>(x)]+y<sub>3</sub>(x)
而y<sub>1</sub>(x)-y<sub>3</sub>(x)、y<sub>2</sub>(x)-y<sub>3</sub>(x)都是齐次的解,但y<sub>3</sub>(x)不是齐次的解
故选项D错误
故选:B.本回答被网友采纳