If $a^{3}+b^{3} =217 $ and $a + b = 7$,

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Target Exam

CUET

Subject

General Test

Chapter

Quantitative Reasoning

Topic

Algebra

Question:

If $a^{3}+b^{3} =217 $ and $a + b = 7$, then the value of $ab$ is :

Options:

-6

-1

Correct Answer:

Explanation:

If $a^{3}+b^{3} =217 $

$a + b = 7$,

then the value of $ab$

(a + b)³ = a³ + b³ + 3ab(a+b)

(7)³ = 217 + 3ab(7)

343 = 217 + 21ab

126 = 21ab

ab = 6