In the following, determine the value(s) of constant(s) involved in the definition so that the given function is continuous: (iii) f(x)=\left\{\begin{array}{c}k\left(x^{2}+3 x\right) \text { if } x<0 \\ \cos 2 x, \text { if } x \geq 0\end{array}\right. (i v) f(x)=\left\{\begin{array}{c}2 \text { if } x \leq 3 \\ a x+b, \text { if } 3<x<5 \\ 9, \text { if } x \geq 5\end{array}\right.
In the following, determine the value(s) of constant(s) involved in the definition so that the given function is continuous: (iii) f(x)=\left\{\begin{array}{c}k\left(x^{2}+3 x\right) \text { if } x<0 \\ \cos 2 x, \text { if } x \geq 0\end{array}\right. (i v) f(x)=\left\{\begin{array}{c}2 \text { if } x \leq 3 \\ a x+b, \text { if } 3<x<5 \\ 9, \text { if } x \geq 5\end{array}\right.

(iii)

A real function f is said to be continuous at x = c, where c is any point in the domain of f if

RD Sharma Solutions for Class 12 Maths Chapter 9 Continuity Image 187

h is a very small positive number. i.e. left hand limit as x → c (LHL) = right hand limit as x → c (RHL) = value of function at x = c.

A function is continuous at x = c if

RD Sharma Solutions for Class 12 Maths Chapter 9 Continuity Image 188

To find the value of constants always try to check continuity at the values of x for which f(x) is changing its expression.

As most of the time discontinuities are here only, if we make the function continuous here, it will automatically become continuous everywhere

From equation 1, it is clear that f(x) is changing its expression at x = 0

Given, f (x) is continuous everywhere

RD Sharma Solutions for Class 12 Maths Chapter 9 Continuity Image 189

since, above equality never holds true for any value of k

k = not defined

=> f (x) will always have a discontinuity at x = 0

(iv)

A real function f is said to be continuous at x = c, where c is any point in the domain of f if

https://gradeup-question-images.grdp.co/liveData/PROJ23776/1543472540835883.png

h is a very small positive number. i.e. left hand limit as x → c (LHL) = right hand limit as x → c (RHL) = value of function at x = c.

A function is continuous at x = c if

RD Sharma Solutions for Class 12 Maths Chapter 9 Continuity Image 192

From equation 1,  f(x) is changing its expression at x = 3

Given, f(x) is continuous everywhere

RD Sharma Solutions for Class 12 Maths Chapter 9 Continuity Image 193

∴ 3a + b = 2 ……………….Equation 2

f(x) is also changing its expression at x = 5

Given, f(x) is continuous everywhere

RD Sharma Solutions for Class 12 Maths Chapter 9 Continuity Image 194