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Question
If x = − 3, find the value of 2x3 + 8x2 – 15.
Sum
Solution
x = − 3
∴ 2x3 + 8x2 – 15
= 2 (– 3)3 + 8 (– 3)2 – 15
= 2 (– 27) + 8 (9) – 15
= – 54 + 72 – 15
= – 54 – 15 + 72
= – 69 + 72
= 3
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Concept of Substitution
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