Question

Subtract b(b2 + b – 7) + 5 from 3b2 – 8 and find the value of expression obtained for
b=-3.​

Answer 1

Answer:

Step-by-step explanation:

b(b2+b-7)

b3+b2+7b

Subtract

3b2-8

b2. +b3+7b

- - -

_____________

2b2-8-b3-7b

Putting the value of b =3

2(9)-8-27-7(3)

18-8-27-21

10-48

-38

Answer 2

The value of expression obtained after subtracting and substituting the value of b as -3 is 11.

Step-by-step explanation:

We need to subtract $b(b^2 + b -7) + 5$ from $3b^2 - 8$.

It can be done in the following way:

$3b^2 - 8$ - [$b(b^2 + b -7) + 5$]

= $3b^2 - 8 - (b^3 + b^2 -7b +5)$

Opening the bracket, we obtain

= $3b^2 - 8 - b^3 -b^2 + 7b - 5$

Rearranging, we get,

= $- b^3 + 3b^2 -b^2 + 7b - 8 - 5$

= $- b^3 + 2b^2 + 7b - 13$

Now, substituting the value of b = -3 in the equation,

= $-(-3)^3 + 2(-3)^2 + 7(-3) -13$

= -(-27) + 2(9) -21 -13

= 27 + 18 -34

= 45 -34

= 11