Question

If $x+y=7,xy=0$, then find $x^3+y^3$.

• A. $131$
• B. $133$
• C. $343$
• D. $-131$

Answer 1

The correct option is C $343$

Given: $x+y=7$
Cubing both sides, we get
$(x+y{)}^3=7^3$
or $x^3+y^3+3xy(x+y)=343$ {Using standard cubic identity}
or $x^3+y^3+3\times 0\times 7=343$ {$\because xy=0$}
or $x^3+y^3=343$