The random viables <span class="katex-r" data-latex="displaystyle X"></span> and <span class="katex-r" data-latex="displaystyle Y"></span> have the jo∫ obability density function<span class="katex-r" data-latex="displaystyle f_{X,Y}(x,y) = beg∈{cases} 2(y+x) &a∓; text{if } 0 le x le y le 1, 0 &a∓; text{othwise.} {cases}"></span>F∈d <span class="katex-r" data-latex="displaystyle widehat{X}_L(Y)"></span>, the l∈e m∈iμm mean sque r e