Question 87

If $$a^{3} + b^{3}$$ = 19 and ab = -6 , then what is the value of a + b?

Solution

$$a^{3}+b^{3}=(a+b)^{3}-3ab(a+b)$$

$$19=(X)^{3}-3(-6)(X)$$

$$X^{3}+18X-19=0$$

by option verification, only X = 1 satisfies the above equation.

so the answer is option C.

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