If $f: R \rightarrow R$ defined by $$ f(x)=\left\{\begin{array}{cc} a^2 \cos ^2 x+b^2 \sin ^2 x, & x \leq 0…

If $f: R \rightarrow R$ defined by $$ f(x)=\left\{\begin{array}{cc} a^2 \cos ^2 x+b^2 \sin ^2 x, & x \leq 0 \\ e^{a x+b}, & x>0 \end{array}\right. $$ is a continuous function, then
  1. $b=2 \log |a|$
  2. $2 b=\log |a|$
  3. $b=\log |2 a|$
  4. $b^2=\log |a|$

Solution

We have, $ \begin{aligned} & \lim _{h \rightarrow 0} f(0+h)=\lim _{h \rightarrow 0} e^{a h+b}=e^b \\ & \text { and } \lim _{h \rightarrow 0} f(0-h)=\lim _{h \rightarrow 0} a^2 \cos ^2 h \\ &+b^2 \sin ^2 h=a^2 0 \\ & \text { Thus, } \quad e^b=a^2 \\ & b=2 \log |a| \end{aligned} $

Asked in: AP EAMCET 2002

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