## Book: RD Sharma - Mathematics (Volume 1)

### Chapter: 9. Continuity

#### Subject: Maths - Class 12th

##### Q. No. 19 of Exercise 9.1

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19
##### Determine the value of the constant k so that the function is continuous at x = 1.

Ideas required to solve the problem:

1. Meaning of continuity of function – If we talk about a general meaning of continuity of a function f(x) , we can say that if we plot the coordinates (x , f(x)) and try to join all those points in the specified region, we can do so without picking our pen i.e you will put your pen/pencil on graph paper and you can draw the curve without any breakage.

Mathematically we define the same thing as given below:

A function f(x) is said to be continuous at x = c where c is x–coordinate of the point at which continuity is to be checked

If:–

…… equation 1

where h is a very small positive no (can assume h = 0.00000000001 like this )

It means :–

Limiting value of the left neighbourhood of x = c also called left hand limit LHL must be equal to limiting value of right neighbourhood of x= c called right hand limit RHL and both must be equal to the value of f(x) at x=c i.e. f(c).

Thus, it is the necessary condition for a function to be continuous

So, whenever we check continuity we try to check above equality if it holds true, function is continuous else it is discontinuous.

Given,

…….equation 2

We need to find the value of k such that f(x) is continuous at x = 1

Since f(x) is continuous at x = 1

(LHL as x tends to 1) = (RHL as x tends to 1) = f(1)

As, f(1) = k [from equation 2]

We can find either LHL or RHL to equate with f(1)

Let’s find RHL,you can find LHL also.

RHL =

=

As, f(x) is continuous

RHL = f(1)

k = –1

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