12th Class Mathematics Sample Paper Mathematics Sample Paper-14

  • question_answer
    Write the value of a for which \[f(x)=\left\{ \begin{matrix}    5x-4, & 0<x\le 1  \\    4{{x}^{2}}+3ax, & 1<x<2  \\ \end{matrix} \right.\] is continuous at x = 1?

    Answer:

    We have, \[f\,(x)=\left\{ \begin{matrix}    5x-4 & 0<x\le 1  \\    4{{x}^{2}}+3ax, & 1<x<2  \\ \end{matrix} \right.\] Here,     \[f\,(1)=5\,(1)-4=1\] \[\therefore \]      \[=\int_{0}^{1}{{{e}^{x-{{[x]}_{dx}}}}}+\int_{1}^{2}{{{e}^{(x-1)}}dx}\] \[=\underset{h\,\,\to \,\,0}{\mathop{\lim }}\,4\,{{(1+h)}^{2}}+3a\,(1+h)=4+3a\] and       \[\underset{x\,\,\to \,\,{{1}^{-}}}{\mathop{\lim }}\,f\,(x)=\underset{h\,\,\to \,\,0}{\mathop{\lim }}\,f\,(1-h)\] \[=\underset{h\,\,\to \,\,0}{\mathop{\lim }}\,5\,(1-h)-4=1\]             \[\therefore \]\[f\,(x)\]is continuous at x = 1.             \[\therefore \]      \[\underset{x\,\,\to \,\,{{1}^{+}}}{\mathop{\lim }}\,f\,(x)=\underset{x\,\,\to \,\,{{1}^{-}}}{\mathop{\lim }}\,f\,(x)=f\,(1)\]             \[\Rightarrow \]               \[4+3a=1\]             \[\Rightarrow \]               \[a=\frac{1-4}{3}=-\,1\]             \[\therefore \]For \[a=-\,1\]the given function is continuous at x = 1.


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