Kindly explain to me how to do part (a).tell me about the concepts behind it also, because i am not very sure about the it.thanks.
vector AB= (pv of B)-(pv of A)=(3i+j)-(-i-j)=4i+2j
similarly find othr vectors
BC=-2i+j
CD=-2i-j
DA=0i-2j
we can see that AB =-2 times CD
so arms AB and DC are parallel
length of AB=|AB|=sqrt[20]
length of CD=|CD|=sqrt[5]