[tex]\boxed { \boxed {(a + b)^2 = a^2 + 2ab + b^2}}[/tex]
[tex](x + y) ^2 = 105[/tex]
[tex]x^2 + 2xy + y^2 = 105[/tex]
[tex]x^2 + y^2 + 2xy = 105[/tex]
[tex]\text{Given that } x^2 + y^2 = 65,[/tex]
[tex]65 + 2xy = 105[/tex]
[tex]2xy = 105 - 65[/tex]
[tex]2xy = 40[/tex]
[tex]xy = 20[/tex]
[tex]\boxed { \boxed {\text{Answer: xy = 20}}}[/tex]
