a) $QE\parallel NP(\bot Oy)$
$PQ\parallel MN(\bot Ox)$.
b) $\Delta OQE$ là tam giác vuông vì có $\widehat{OEQ}=90^o$
$\Rightarrow \widehat{EOQ}=90^o-\widehat{OQE}=90^o-40^o=50^o$
$\Delta OQP$ là tam giác vuông vì có $\widehat{OQP}=90^o$
$\Rightarrow \widehat{OPQ}=90^o-\widehat{EOQ}=90^o-50^o=40^o$
$\widehat{EQP}=90^o-\widehat{OQE}=90^o-40^o=50^o$
$\widehat{OPN}=90^o-\widehat{OPQ}=90^o-40^o=50^o$
$\widehat{ONP}=\widehat{OQE}=40^o$ (so le)