# QUESTIONS ON LINEAR FUNCTIONS

Question 1 :

Let f = {(-1, 3), (0, -1), (2, -9)} be a linear function from Z into Z . Find f(x).

Let the linear function be f(x) = ax + b.

From the ordered pair (-1, 3), x = -1, f(x) = 3.

3 = a(-1) + b

3 = -a + b ----(1)

From the ordered pair (0, -1), x = 0, f(x) = -1.

-1 = a(0) + b

-1 = b

Substitute b = -1 in (1).

3 = -a + (-1)

3 = -a - 1

3 + a = -1

Subtract 3 from each side.

a = -4

So, the linear function is f(x) = -4x - 1.

Question 2 :

In electrical circuit theory, a circuit C(t) is called a linear circuit if it satisfies the superposition principle given by C(at1 + bt2) = aC(t1) + bC(t2), where a, b are constants. Show that the circuit C(t) = 3t is linear.

Take two points t1 and t2 from domain of C(t).

C(at1) =  aC(t1)

C(at2) =  aC(t2)

It is given that C(t) = 3t.

C(t) = 3t

C(atbt2)  =  3(at+ at2)

C(atbt2)  =  3at+ 3at2

C(atbt2)  =  a(3t1+ a(3t2)

C(atbt2)  =  aC(t1aC(t2)

Superposition principle is satisfied.

Hence c(t) = 3t is linear.

Question 3 :

The cost of a school banquet is \$95 plus \$15 for each person attending. Write a linear function that gives total cost of the number of people attending. What is the cost for 77 people?

Solution :

Let f(x) be the total cost and x be the number of persons attending the banquet.

Linear function that gives total cost :

f(x) = 95 + 15x

To find the cost for 77 people, substitute x = 77.

f(77) = 95 + 15(77)

= 95 + 1155

= 1250

So, the total cost of attending 77 people is \$1250.

Question 4 :

A manufacturer produces 80 units of a particular product at a cost of \$ 220000 and 125 units at a cost of \$ 287500. Assuming the cost curve to be linear, find the cost of 95 units.

Solution :

Because the cost curve is linear, the function which best fits the given information will be a linear-cost function.

y = Ax + B

y ----> Total cost

x ----> Number of units

Target : To find the value of y when x = 95.

From the question, we have

x = 80 and y = 220000

x = 75 and y = 287500

Substitute the above values for x and y in 'y = Ax + B'.

220000 = 80A + B

287500 = 75A + B

Solve for x and y.

A = 1500 and B = 100000

The linear cost function :

y = 1500x + 100000

Substitute x = 95.

y = 1500x + 100000

y = 1500x95 + 100000

y = 142500  +  100000

y = 242500

So, the cost of 95 units is \$242500.

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