MHT CET · Maths · Application of Derivatives
If Rolle's theorem holds for the function \(f(x)=x^3+b x^2+a x+5\) on \([1,3]\) with \(c=2+\frac{1}{\sqrt{3}}\), then the values of \(a\) and \(b\) respectively are
- A \(-11,-6\)
- B 11,6
- C \(11,-6\)
- D 6,11
Answer & Solution
Correct Answer
(C) \(11,-6\)
Step-by-step Solution
Detailed explanation
Since \(\mathrm{f}(x)\) satisfies the Rolle's theorem,
\(f(1)=f(3)\)
\(\therefore \quad 1+b+a+5=27+9 b+3 a+5\)
\(\Rightarrow 2 a+8 b=-26\)
\(\Rightarrow a+4 b=-13\) ...(i)
\(\vec{f}(x)=x^3+b x^2+a x+5\)
\(\therefore \quad \mathrm{f}^{\prime}(x)=3 x^2+2 \mathrm{~b} x+\mathrm{a}\)
Now, \(\mathrm{f}^{\prime}(\mathrm{c})=0\)
\(
\begin{aligned}
& \Rightarrow \mathrm{f}^{\prime}\left(2+\frac{1}{\sqrt{3}}\right)=0 \\
& \Rightarrow 3\left(2+\frac{1}{\sqrt{3}}\right)^2+2 \mathrm{~b}\left(2+\frac{1}{\sqrt{3}}\right)+\mathrm{a}=0 \\
& \Rightarrow 3\left(4+\frac{4}{\sqrt{3}}+\frac{1}{3}\right)+4 \mathrm{~b}+\frac{2 \mathrm{~b}}{\sqrt{3}}+\mathrm{a}=0 \\
& \Rightarrow \mathrm{a}+4 \mathrm{~b}+\frac{2 \mathrm{~b}+12}{\sqrt{3}}+13=0 \\
& \Rightarrow-13+\frac{2 \mathrm{~b}+12}{\sqrt{3}}+13=0 \\
& \Rightarrow \frac{2 \mathrm{~b}+12}{\sqrt{3}}=0 \\
& \Rightarrow \mathrm{b}=-6
\end{aligned}
\)
Substituting \(b=-6\) in (i), we get \(a=11\)
\(f(1)=f(3)\)
\(\therefore \quad 1+b+a+5=27+9 b+3 a+5\)
\(\Rightarrow 2 a+8 b=-26\)
\(\Rightarrow a+4 b=-13\) ...(i)
\(\vec{f}(x)=x^3+b x^2+a x+5\)
\(\therefore \quad \mathrm{f}^{\prime}(x)=3 x^2+2 \mathrm{~b} x+\mathrm{a}\)
Now, \(\mathrm{f}^{\prime}(\mathrm{c})=0\)
\(
\begin{aligned}
& \Rightarrow \mathrm{f}^{\prime}\left(2+\frac{1}{\sqrt{3}}\right)=0 \\
& \Rightarrow 3\left(2+\frac{1}{\sqrt{3}}\right)^2+2 \mathrm{~b}\left(2+\frac{1}{\sqrt{3}}\right)+\mathrm{a}=0 \\
& \Rightarrow 3\left(4+\frac{4}{\sqrt{3}}+\frac{1}{3}\right)+4 \mathrm{~b}+\frac{2 \mathrm{~b}}{\sqrt{3}}+\mathrm{a}=0 \\
& \Rightarrow \mathrm{a}+4 \mathrm{~b}+\frac{2 \mathrm{~b}+12}{\sqrt{3}}+13=0 \\
& \Rightarrow-13+\frac{2 \mathrm{~b}+12}{\sqrt{3}}+13=0 \\
& \Rightarrow \frac{2 \mathrm{~b}+12}{\sqrt{3}}=0 \\
& \Rightarrow \mathrm{b}=-6
\end{aligned}
\)
Substituting \(b=-6\) in (i), we get \(a=11\)
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
- A ladder 5 m long rests against a vertical wall. If its top slides downwards at the rate of \(10 \mathrm{~cm} / \mathrm{sec}\)., then the foot of the ladder is sliding at the rate of _______ \(\mathrm{m} / \mathrm{sec}\), when it is 4 m away from the wall.MHT CET 2024 Easy
- If \(\mathrm{f}(x)= \begin{cases}-2 \sin x & , \quad x \leqslant-\frac{\pi}{2} \\ a \sin x+\mathrm{b} & , \quad \frac{-\pi}{2} < x < \frac{\pi}{2} \\ \cos x & , \quad x \geqslant \frac{\pi}{2}\end{cases}\) is continuous at \(\mathrm{x}=\frac{-\pi}{2}\) and \(x=\frac{\pi}{2}\), then the value of \(2 a+\mathrm{b}\) isMHT CET 2025 Medium
- For a \(3 \times 3\) matrix A, if \(\mathrm{A}(\operatorname{adj} \mathrm{A})=\left[\begin{array}{ccc}-10 & 0 & 0 \\ 0 & -10 & 2 \\ 0 & 0 & -10\end{array}\right]\), then the value of determinant of \(\mathrm{A}\) isMHT CET 2021 Easy
- An experiment succeeds twice as often as it fails. Then the probability, that in the next 6 trials there will be atleast 4 successes, isMHT CET 2023 Easy
- \(|\vec{a}|=\sqrt{3},|\vec{b}|=5, \vec{b} \cdot \vec{c}=10\) and angle between \(\bar{b}\) and \(\bar{c}\) is \(\left(\frac{\pi}{3}\right)\). If \(\vec{a}\) is perpendicular to \(\vec{b} \times \vec{c}\), then value of \(|\vec{a} \times(\vec{b} \times \vec{c})|\) isMHT CET 2022 Medium
- A wet substance in the open air loses its moisture at a rate proportional to the moisture content. If a sheet hung in the open air loses half its moisture during the first hour, then the time t , in which \(99 \%\) of the moisture will be lost, isMHT CET 2024 Hard
More PYQs from MHT CET
- If two alleles for a particular trait in an organism are identical, it is called __________MHT CET 2024 Easy
- What is IUPAC name of the compound?
MHT CET 2023 Easy - The volume of a metal block increases by \(0.225 \%\) when its temperature is increased by \(30^{\circ} \mathrm{C}\). Hence coefficient of linear expansion of the material of metal block isMHT CET 2023 Medium
- Which carbon atom of glucopyranose numbered from \(\mathrm{C}-1\) to \(\mathrm{C}-6\) is anomeric?MHT CET 2025 Easy
- The line MN whose equation is \(x-y-2=0\) cuts the X-axis at M and co-ordinates of N are \((4,2)\). The line MN is rotated about M through \(45^{\circ}\) in anticlockwise direction. The equation of the line MN in the new position isMHT CET 2025 Medium
- A person with machine gun can fire \(50 \mathrm{~g}\) bullets with a velocity of \(240 \mathrm{~m} / \mathrm{s}\). A \(60 \mathrm{~kg}\) tiger moves towards him with a velocity of \(12 \mathrm{~m} / \mathrm{s}\). In order to stop the tiger in track, the number of bullets the person fires towards the tiger isMHT CET 2023 Medium