1.Relation and Function
hard

Let $\mathrm{f}(\mathrm{x})$ be a polynomial of degree $3$ such that $\mathrm{f}(\mathrm{k})=-\frac{2}{\mathrm{k}}$ for $\mathrm{k}=2,3,4,5 .$ Then the value of $52-10 \mathrm{f}(10)$ is equal to :

A

$26$

B

$36$

C

$52$

D

$87$

(JEE MAIN-2021)

Solution

$\mathrm{k}\, \mathrm{f}(\mathrm{k})+2=\lambda(\mathrm{x}-2)(\mathrm{x}-3)(\mathrm{x}-4)(\mathrm{x}-5) \ldots(1)$

put $\mathrm{x}=0$

we get $\lambda=\frac{1}{60}$

Now put $\lambda$ in equation $(1)$

$\Rightarrow \mathrm{k\,f}(\mathrm{k})+2=\frac{1}{60}(\mathrm{x}-2)(\mathrm{x}-3)(\mathrm{x}-4)(\mathrm{x}-5)$

Put $\mathrm{x}=10$

$\Rightarrow 10 \,\mathrm{f}(10)+2=\frac{1}{60}(8)(7)(6)(5)$

$\Rightarrow 52-10 \,\mathrm{f}(10)=52-26=26$

Standard 12
Mathematics

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