Question

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

Answer 1

We have,

Required difference = (3b² – 8) – [b(b² + b – 7) + 5]

= 3b² – 8 – b(b² + b – 7) – 5

= 3b² – 8 – b³ – b² + 7b – 5

= – b³ + 2b² + 7b – 13

Now, If b = – 3

The value of above expression = – (–3)³ + 2(–3)² + 7(–3) – 13

= – (–27) + 2 × 9 – 21 – 13

= 27 + 18 – 21 – 13

= 45 – 34

= 11