Question

If $x+y=8$ and $xy=7$ then the value of $x^3+y^3$ is

• A. 344
• B. 342
• C. 345
• D. 340

Answer 1

The correct option is A 344

Since, $(x+y{)}^3=x^3+y^3+3xy(x+y)$ we have

$x^3+y^3=(x+y{)}^3-3xy(x+y)$

Given, $x+y=8$ and $xy=7$

by substituting the values in the equation

$\Rightarrow x^3+y^3=(8{)}^3-3(7\left)\right(8)$

$=512-168=344$.

$\Rightarrow x^3+y^3=344$

Option $A$ is correct.