Question

2. If x= 2 - 21/3 + 22/3, then the
value of x- 6x2 + 18x + 18 is
(2) 33
(3) 40
(4) 45
(1) 22​

Answer 1

Answer:

3 is correct

Step-by-step explanation:

x = 2 - 21 / 3 + 22 / 3

⇒ x – 2 = 22 / 3 - 21 / 3

On cubing both sides ,

⇒ x3 - 3x2 × 2 + 3x × 4 – 8 = ( 22 / 3 )3 - ( 21 / 3 )3 - 3 . 22 / 3 . 21 / 3( 22 / 3 - 21 / 3 )

⇒ x3 - 6x2 + 12x – 8 = = 4 – 2 – 6 (x – 2)

⇒ x3 - 6x2 + 12x – 8 = = 2 – 6x + 12

⇒ x3 - 6x2 + 18x + 18 = 2 + 12 + 8 + 18 = 40

Answer 2

Answer:

3

Step-by-step explanation:

x=2+2 2/3+2 1/3

x=2+8/3+7/3

x=2+15/3

x=2+5=7

now, x3-6x2+6x

=7^3-6×7^2+6×7

=343-294+42

=91