Question 93

If a+b = 8 and ab =15, then $$a^{3} + b^{3}$$ is

Solution

It is given that : $$(a+b)=8$$ and $$ab=15$$

Using the expression, $$(a^3+b^3)=(a+b)(a^2+b^2-ab)$$

= $$(8)(a^2+b^2-15)$$

Also, $$(a^2+b^2)=(a+b)^2-2ab$$

= $$8[((a+b)^2-2ab)-15]$$

= $$8[(8^2-(2 \times 15))-15]$$

= $$8(64-30-15) = 8 \times 19$$

= $$152$$

=> Ans - (C)

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