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EM - I


Unit – 5



Unit – 5


Algebra of Complex numbers and Roots of polynomial Equations

Q 1: Simplify 16 i+10i (3-i)

Solution:

Given,

16i +10i (3-i)

=16i+10i(3i) +10i(-i)

=16i+30i-10i2

=46i-10(-1)

=46i+10

Here real part is 10 and imaginary part is 46

 

Q 2: Express the following into a+ib form

Solution:

Given., 


z   =      = = + i

Modulus, = =

Conjugate = (  - 

 

Q 3: Find the polar form of 7-5j

Solution:

We need to find r and

r=

=

=

= 8.6

To find θ, we first find the acute angle α ,

= tan-1()

   =   tan-1( )

    = 35.540

7-5j is in the fourth quadrant so we we have,

= 3600 -35.540 = 324.460

So, expressing 7-5j in the polar form as.,

7-5j = 8.6(cos324.50 +j sin324.50)

 

Q 4: Represent 1+j in polar form

= arctan =600

Solution: R=   = =2

So,

1+j = 2 600 = 2(cos600 +jsin 600)

 

Q 5: Write ( ) 7 in the form of a+ib

First determine the radius ie., r

Solution: Let r=

r = + i2

r=

r=2

Now cos =- and sin = , must be in the first quadrant and =300

Therefore,

( ) 77

( ) 7 = 27 [cos 7.300 +i sin 7.300]

        = 128[cos 2100+isin2100]

= 28 +i

( ) 7 = 64 -64 i

 

Q 6: Write ( +i )4 in the form of a+ib

Solution: First, we determine the radius,

r =

r=

r=

r=2

Now,

( +i )4 = 4

        = [24 (cos 4.3150 + isin 4.3150)

        =16(cos 21600+i sin 21600)

        = 16( cos 1800+i.sin 1800)

        = 16(-1+0i)

        = -16

 

Q 7: Prove that function is analytic function.

Solution: Real and Imaginary parts of are

If,

On differentiating u,v we get

Again differentiating

Hence e-R-Equation satisfies.

 

Q 8: 2y=4x16 and y=2x8 perpendicular.

 

Solution: Let 2y =4x-16 (1)

       Y=2x-8    (2)

 

Let s write equation (1) in the form of y= mx+c and 2)

 

y= 2x-8 and y = 2x-8

 

Here we see that there is only one line,

But if there are two lines, they would have been parallel as the gradients are same.

y= 2x+5 and y= 2x-8 are parallel

y= -- x-8 and y=2x-8 are perpendicular

-- are perpendicular.

 

Q 9: Lisa will make up a punch that is 25% fruit juice by adding pure fruit-juice to a

2-liter mixture that is 10% pure fruit-juice. How many litres of pure fruit juice does she need to add?

Solution:

Let’s call the amount to be found z

Then you will end up with x+2L of 25% juice

This will contain 0.25(x+2) =0.25x+0.5pure juice

The original 2L already contained 0.10.2=0.2 juice

So we added 0.25x=0.3 juice, but this is also x(as x=100% juice).

0.25x+0.3=x 0.75x=0.3 x=0.4 liter

 

Q10: Finding the real root of the following polynomial equation using cardano’s method

 

  X3+2x2+3x+4=0

 

Solution: Given that., a=1, b=2, c=3, d=4

 

Compute Q and R:

 

   Q= =

 

R= =

Compute S and T :

 

S= =

T= =

 

Compute the roots:

  X1 =  S+T-

 

=

=  -1.651

 

X2 = - +i (s-t)

 

    = + i.

 

X3 =   - +i (s-t)

  - i.

  -0.175  -1.547 i.

Given quadratic equation: 36x4 -72x3-391x2-123x+270

Applying Ferrari’s method:

We have,

A=36,  B=-72,  C=-391,  D=-123, E=270

- =-

 

- + = -

- - + =

P=  - = =15.62 16

Q= - - = - =23.5924

Finally,

R= -   = -

By solving the above equation, we get., 12 .

 

Q 11: Consider the quadratic equation y4+ay3+by2+cy+d=0

Solution: By substituting y= x- the above equation will be reduced to the following

=X4+ px2+qz+r=0,(1)

The above equation doesn’t contain x3., if one introduces an auxiliary parameter ,then the left hand side of equation (1)  can be written as follows:

=X4+ px2+qz+r = (x2 + + )2 – [2ax2 –qx+( 2 +p + -r)](2)

= q2 -4.2 ( 2 +p + –r) =0

Then the required equation for = 0 the polynomial in square brackets in equation (2) has one double root

X0=

 



Unit – 5


Algebra of Complex numbers and Roots of polynomial Equations

Q 1: Simplify 16 i+10i (3-i)

Solution:

Given,

16i +10i (3-i)

=16i+10i(3i) +10i(-i)

=16i+30i-10i2

=46i-10(-1)

=46i+10

Here real part is 10 and imaginary part is 46

 

Q 2: Express the following into a+ib form

Solution:

Given., 


z   =      = = + i

Modulus, = =

Conjugate = (  - 

 

Q 3: Find the polar form of 7-5j

Solution:

We need to find r and

r=

=

=

= 8.6

To find θ, we first find the acute angle α ,

= tan-1()

   =   tan-1( )

    = 35.540

7-5j is in the fourth quadrant so we we have,

= 3600 -35.540 = 324.460

So, expressing 7-5j in the polar form as.,

7-5j = 8.6(cos324.50 +j sin324.50)

 

Q 4: Represent 1+j in polar form

= arctan =600

Solution: R=   = =2

So,

1+j = 2 600 = 2(cos600 +jsin 600)

 

Q 5: Write ( ) 7 in the form of a+ib

First determine the radius ie., r

Solution: Let r=

r = + i2

r=

r=2

Now cos =- and sin = , must be in the first quadrant and =300

Therefore,

( ) 77

( ) 7 = 27 [cos 7.300 +i sin 7.300]

        = 128[cos 2100+isin2100]

= 28 +i

( ) 7 = 64 -64 i

 

Q 6: Write ( +i )4 in the form of a+ib

Solution: First, we determine the radius,

r =

r=

r=

r=2

Now,

( +i )4 = 4

        = [24 (cos 4.3150 + isin 4.3150)

        =16(cos 21600+i sin 21600)

        = 16( cos 1800+i.sin 1800)

        = 16(-1+0i)

        = -16

 

Q 7: Prove that function is analytic function.

Solution: Real and Imaginary parts of are

If,

On differentiating u,v we get

Again differentiating

Hence e-R-Equation satisfies.

 

Q 8: 2y=4x16 and y=2x8 perpendicular.

 

Solution: Let 2y =4x-16 (1)

       Y=2x-8    (2)

 

Let s write equation (1) in the form of y= mx+c and 2)

 

y= 2x-8 and y = 2x-8

 

Here we see that there is only one line,

But if there are two lines, they would have been parallel as the gradients are same.

y= 2x+5 and y= 2x-8 are parallel

y= -- x-8 and y=2x-8 are perpendicular

-- are perpendicular.

 

Q 9: Lisa will make up a punch that is 25% fruit juice by adding pure fruit-juice to a

2-liter mixture that is 10% pure fruit-juice. How many litres of pure fruit juice does she need to add?

Solution:

Let’s call the amount to be found z

Then you will end up with x+2L of 25% juice

This will contain 0.25(x+2) =0.25x+0.5pure juice

The original 2L already contained 0.10.2=0.2 juice

So we added 0.25x=0.3 juice, but this is also x(as x=100% juice).

0.25x+0.3=x 0.75x=0.3 x=0.4 liter

 

Q10: Finding the real root of the following polynomial equation using cardano’s method

 

  X3+2x2+3x+4=0

 

Solution: Given that., a=1, b=2, c=3, d=4

 

Compute Q and R:

 

   Q= =

 

R= =

Compute S and T :

 

S= =

T= =

 

Compute the roots:

  X1 =  S+T-

 

=

=  -1.651

 

X2 = - +i (s-t)

 

    = + i.

 

X3 =   - +i (s-t)

  - i.

  -0.175  -1.547 i.

Given quadratic equation: 36x4 -72x3-391x2-123x+270

Applying Ferrari’s method:

We have,

A=36,  B=-72,  C=-391,  D=-123, E=270

- =-

 

- + = -

- - + =

P=  - = =15.62 16

Q= - - = - =23.5924

Finally,

R= -   = -

By solving the above equation, we get., 12 .

 

Q 11: Consider the quadratic equation y4+ay3+by2+cy+d=0

Solution: By substituting y= x- the above equation will be reduced to the following

=X4+ px2+qz+r=0,(1)

The above equation doesn’t contain x3., if one introduces an auxiliary parameter ,then the left hand side of equation (1)  can be written as follows:

=X4+ px2+qz+r = (x2 + + )2 – [2ax2 –qx+( 2 +p + -r)](2)

= q2 -4.2 ( 2 +p + –r) =0

Then the required equation for = 0 the polynomial in square brackets in equation (2) has one double root

X0=