SSC CGL 12 June 2019 Shift-1

Question 67

If (a + b) = 6 and ab = 8, then $$(a^3 + b^3)$$ is equal to:

Solution

Given that,

$$a+b=6 $$ and $$ ab=8$$

We know that,

$$(a+b)^3=a^3+b^3+3ab(a+b)$$

$$\Rightarrow (6)^3=a^3+b^3+3\times8\times(6)$$

$$\Rightarrow 216=a^3+b^3+144$$

$$\Rightarrow a^3+b^3=216-144=72$$

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