Subtract b (b² + b - 7) + 5 from 3b² - 8 and find the value of expression obtained for b = -3.
Solution:
Given, subtract b(b² + b - 7) + 5 from 3b² - 8
⇒ (3b² - 8) - [b(b² + b - 7) + 5]
= (3b² - 8) - [b³ + b² - 7b + 5]
= 3b² - 8 - b³ - b² + 7b - 5
= -b³ + 3b² - b² + 7b - 8 - 5
= -b³ + 2b² + 7b - 13
Now, substituting b = -3,
= -b³ + 2b² + 7b - 13
= -(-3)³ + 2(-3)² + 7(-3) - 13
= 27 + 18 - 21 - 13
= 11
✦ Try This: Subtract: x(2x² + 3x - 17) + 5 from 5x² - 9x + 21 and find the value of expression obtained for x = - 2.
Given, subtract x (2x² + 3x - 17) + 5 from 5x² - 9x + 21
⇒ 5x² - 9x + 21 - {x (2x² + 3x - 17) + 5}
= 5x² - 9x + 21 - 2x³ - 3x² + 17x - 5
= -2x³ + 2x² + 8x + 16
Now substituting x = -2
= -2(-2)³ + 2(-2)² + 8(-2) + 16
= 16 + 8 - 16 + 16 = 24
☛ Also Check: NCERT Solutions for Class 8 Maths Chapter 9
NCERT Exemplar Class 8 Maths Chapter 7 Problem 116
Subtract b (b² + b - 7) + 5 from 3b² - 8 and find the value of expression obtained for b = -3.
Summary:
Subtracting b (b² + b - 7) + 5 from 3b² - 8, we get -b³ + 2b² + 7b - 13 and the value of expression obtained for b = -3 is 11
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