How to show it is a rhombus I am trying to solve question 2 (figure 2). I have shown that the diagonals are interesting each other in right angle but I cannot show that AB||GH. Please help.

Note:
$$mBAG=mGAH=mBGA \Rightarrow \Delta ABG \ \text{is isosceles},$$
$$mGBH=mBHA=mHBA \Rightarrow \Delta ABH \ \text{is isosceles}.$$
Since $BG||AH$ and $BG=AH$, then $AB=GH$ and $AB||GH$.
