In the set $$\mathrm{W}$$ of whole numbers an equivalence relation $$\mathrm{R}$$ is defined as follows $$\mathrm{aRb}$$ iff both $$\mathrm{a}$$ & $$\mathrm{~b}$$ leave the same reminder when divided by 5. The equivalence class of 1 is given by.
$$ \text { If } P(B)=\frac{3}{5} \quad P(A / B)=\frac{1}{2} \text { and } P(A \cup B)=\frac{4}{5} \text { then } P(A \cup B)^{\prime}+P\left(A^{\prime} \cup B\right)= $$
$$ \text { The function defined by } f(x)=\left\{\begin{array}{cc} \frac{\sin x}{x}+\cos x & x>0 \\ -5 k & x=0 \\ \frac{4(1-\sqrt{1-x})}{x} & x<0 \end{array} \quad \text { is continous at } x=0, \quad \text { then } k\right. \text { equals } $$
$$ f(x)=2 x-\tan ^{-1} x-\log (x+\sqrt{x^2+1}) \text { is monotonically increasing, when } $$