Question 9 - CBSE Class 12 Sample Paper for 2026 Boards - Solutions of Sample Papers and Past Year Papers - for Class 12 Boards

Last updated at November 26, 2025 by Teachoo

This question is similar to Chapter 6 Class 12 Application of Derivatives - Ex 6.2

Please check the question here

https://www.teachoo.com/13470/709/Ex-6.2--6-b/category/Ex-6.2/

A function 𝑓(𝑥)=10−𝑥−2𝑥^2 is increasing on the interval [Class 12] - CBSE Class 12 Sample Paper for 2026 Boards

part 2 - Question 9 - CBSE Class 12 Sample Paper for 2026 Boards - Solutions of Sample Papers and Past Year Papers - for Class 12 Boards - Class 12

part 3 - Question 9 - CBSE Class 12 Sample Paper for 2026 Boards - Solutions of Sample Papers and Past Year Papers - for Class 12 Boards - Class 12

Next: Question 10 → Remove Ads Share on WhatsApp

Transcript

Question 9 A function 𝑓(𝑥)=10−𝑥−2𝑥^2 is increasing on the interval (A) (−∞,−1/4] (B) (−∞,1/4) (C) [−1/4,∞) (D) [−1/4,1/4]Calculating f’(𝒙) f(𝑥) = 10 – 𝑥 – 2𝑥2 f’(𝑥) = – 1 – 2 × 2𝑥 f’(𝑥) = −(1 + 4𝑥) Putting f’(𝒙) = 0 −1(1 + 4𝑥) = 0 1 + 4𝑥 = 0 4𝑥 = −1 𝒙 = (−𝟏)/𝟒 Plotting points on number line Hence, f is strictly decreasing for 𝒙 > (−𝟏)/𝟒 f is strictly increasing for x < (−𝟏)/𝟒 Since f is strictly increasing for x < (−𝟏)/𝟒 Therefore, f is increasing for x ≤ (−𝟏)/𝟒 We write f is increasing in (−∞,−1/4] So, the correct answer is (A)

Made by

Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 15 years. He provides courses for Maths, Science and Computer Science at Teachoo

Class 6

Class 7

Class 8

Class 9

Class 10

Class 11

Class 12

Courses

Interesting

Popular