Question

Let a and b be the roots of the equation x^2 - 3x - 1 = 0. Find a^3 + b^3

hint: a^3 + b^3 = (a+b)(a^2-ab+b^2)

URGENT PLEASE

Answer 1

Correct option is A)

Given,a,b are distance roots of x

3

+3x

2

−1=0

⇒a

3

+3a

2

−1=0 and b

3

+3b

2

−1=0

let the third root be c

then c

3

+3c

2

−1=0

product of roots =

a

−d

=

1

−(−1)

=1

⇒

abc=1

c=

ab

1

but c is root of x

3

+3x

2

−1=0

⇒c

3

+3x

2

−1=0

⇒

(ab)

3

1

+

(ab)

2

3

−1=0

⇒

1+3ab−(ab)

3

=0

.....(1)

in equation (1)

(ab)

3

−3(ab)−1=0

⇒ab is root of

x

3

−3x−1=0

∴(ab) is root of

x

3

−3x−1=0