问题 单项选择题

设y1(x),y2(x)为二阶常系数齐次线性方程y"+py'+qy=0的两个特解,则c1y1(x)+c2y2(x)(c1,c2为任意常数)是该方程通解的充分必要条件是

A.y1(x)y'2(x)-y2(x)y'1(x)=0.

B.y1(x)y'2(x)-y2(x)y'1(x)≠0.

C.y1(x)y'2(x)+y2(x)y'1(x)=0.

D.y1(x)y'2(x)+y2(x)y'1(x)≠0.

答案

参考答案:B

解析:[分析] 根据题设,y1(x)与y2(x)应线性无关,也就是说[*](常数).反之若这个比值为常数,即y1(x)=λy2(x),则y1(x)与y2(x)线性相关.由y1(x)=λy2(x)可得:y'1(x)=λy'2(x),从而行列式[*],所以y1(x)y'2(x)-y2(x),y'1(x)=0,因此应选(B).

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