MHT CET · Maths · Continuity and Differentiability
If \(\mathrm{f}(x)\) is continuous on its domain \([-2,2]\), where
\(\mathrm{f}(x)= \begin{cases}\frac{\sin a x}{x}+3 , \text { for }-2 \leq x < 0 \ 2 x+7 ,\end{cases}\) \( \text { for } 0 \leq x \leq 1 \ \sqrt{x^2+8}-\mathrm{b}, \text { for } 1 < x \leq 2\)
then the value of \(2 a+3 b\) is
- A \(-12\)
- B \(-10\)
- C 10
- D 12
Answer & Solution
Correct Answer
(B) \(-10\)
Step-by-step Solution
Detailed explanation
Since \(\mathrm{f}(x)\) is continuous in \([-2,2]\), it is continuous at \(x=0\) and \(x=1\).
\(\therefore \quad \lim _{x \rightarrow 0^{-}} \mathrm{f}(x)=\lim _{x \rightarrow 0^{+}} \mathrm{f}(x)\)
\(\Rightarrow \lim _{x \rightarrow 0^{-}}\left(\frac{\sin a x}{x}+3\right)=\lim _{x \rightarrow 0^{+}}(2 x+7)\)
\(\begin{aligned} & \Rightarrow a+3=0+7 \\ & \Rightarrow a=4\end{aligned}\)
Also, \(\lim _{x \rightarrow 1^{-}} \mathrm{f}(x)=\lim _{x \rightarrow 1^{+}} \mathrm{f}(x)\)
\(\Rightarrow \lim _{x \rightarrow 1^{-}}(2 x+7)=\lim _{x \rightarrow 1^{+}}\left(\sqrt{x^2+8}-b\right)\)
\(\begin{aligned} & \Rightarrow 2(1)+7=\sqrt{1+8}-b \\ & \Rightarrow 9=3-b \\ & \Rightarrow b=-6\end{aligned}\)
\(\therefore \quad 2 a+3 b=8-18=-10\)
\(\therefore \quad \lim _{x \rightarrow 0^{-}} \mathrm{f}(x)=\lim _{x \rightarrow 0^{+}} \mathrm{f}(x)\)
\(\Rightarrow \lim _{x \rightarrow 0^{-}}\left(\frac{\sin a x}{x}+3\right)=\lim _{x \rightarrow 0^{+}}(2 x+7)\)
\(\begin{aligned} & \Rightarrow a+3=0+7 \\ & \Rightarrow a=4\end{aligned}\)
Also, \(\lim _{x \rightarrow 1^{-}} \mathrm{f}(x)=\lim _{x \rightarrow 1^{+}} \mathrm{f}(x)\)
\(\Rightarrow \lim _{x \rightarrow 1^{-}}(2 x+7)=\lim _{x \rightarrow 1^{+}}\left(\sqrt{x^2+8}-b\right)\)
\(\begin{aligned} & \Rightarrow 2(1)+7=\sqrt{1+8}-b \\ & \Rightarrow 9=3-b \\ & \Rightarrow b=-6\end{aligned}\)
\(\therefore \quad 2 a+3 b=8-18=-10\)
See the Complete Solution
Get step-by-step explanations for this and 2.5 Lakh+ more JEE, NEET & CET questions.
- Unlock all solutions
- Practice the full chapter
- Track accuracy across PYQs
4.8 rated on Google Play · 14,000+ reviews
More questions from Maths
- Three boxes contain respectively 3 white and 1 black, 2 white and 2 black, 1 white and 3 black balls, from each of the boxes one ball is drawn at random. The probability that 2 white and 1 black balls will be drawn, isMHT CET 2011 Medium
- Let \(\bar{a}=\alpha \hat{i}+3 \hat{\mathrm{j}}-\hat{\mathrm{k}}, \overline{\mathrm{b}}=3 \hat{i}-\hat{\mathrm{j}}+\beta \hat{\mathrm{k}}\) and \(\overline{\mathrm{c}}=\hat{i}+2 \hat{\mathrm{j}}-2 \hat{\mathrm{k}}\) where \(\alpha, \beta \in \mathbb{R}\), be three vectors. If the projection of \(\bar{a}\) on \(\bar{c}\) is \(\frac{10}{3}\) and \(\overline{\mathrm{b}} \times \overline{\mathrm{c}}=-6 \hat{i}+10 \hat{\mathrm{j}}+7 \hat{\mathrm{k}}\), then the value of \((\alpha+\beta)\) is equal toMHT CET 2025 Medium
- Words of length 10 are formed by using the letters A, B, C, D, E, F, G, H, I, J. Let \(x\). be number of such words where no letter is repeated and \(y\) be number of such words where exactly two letters are repeated twice and no other letter is repeated, then the value of \(\frac{y}{x}\) isMHT CET 2024 Hard
- If \(y=\sin \left(2 \tan ^{-1} \sqrt{\frac{1+x}{1-x}}\right)\), then \(\frac{d y}{d x}\) is equal toMHT CET 2022 Easy
- \(\lim _{x \rightarrow \frac{\pi}{2}} \frac{\cot x-\cos x}{(\pi-2 x)^3}\) equalsMHT CET 2023 Easy
- If two sides of a triangle are \(\sqrt{3}-2\) and \(\sqrt{3}+2\) units and their included angle is \(60^{\circ}\), then the third side of the triangle isMHT CET 2025 Easy
More PYQs from MHT CET
- Identify the product ' B ' in the following sequence of reactions.
Methylpropanoate \(\underset{\text { dil. } \mathrm{NaOH}}{\stackrel{\Delta}{\longrightarrow}} \mathrm{A} \xrightarrow[\text { Conc. } \mathrm{HCl}]{\mathrm{H}^{+}} \mathrm{B}\)MHT CET 2025 Medium - In \((0,2 \pi)\), the number of solutions of \(\tan \theta+\sec \theta=2 \cos \theta\) areMHT CET 2024 Easy
- For a reaction \(\Delta \mathrm{H}=-30 \mathrm{~kJ}\) and \(\Delta \mathrm{S}=-45 \mathrm{~J} \mathrm{~K}^{-1}\), at what temperature reaction changes from spontaneous to non spontaneous?MHT CET 2020 Easy
- The area of the region include between the parabolas \(y^2=8 x\) and \(\mathrm{x}^2=8 \mathrm{y}\), isMHT CET 2021 Easy
- ' \(F\) ' is the force between the two identical charged particles placed at a distance ' \(\mathrm{Y}\) ' from each other. If the distance between the charges is reduced to half the previous distance, then force between them becomesMHT CET 2021 Easy
- The order and degree of the differential equation \(\left[1+\left[\frac{d y}{d x}\right]^{3}\right]^{\frac{7}{3}}=7 \frac{d^{2} y}{d x^{2}}\) are respectively.MHT CET 2020 Easy