In quadrilateral song, one pair of opposite sides and one pair of opposite angles are and

Remember in geometry that when any polygon is referred to, the vertices are named in rotational order, either clockwise or counterclockwise, so if you start at S and proceed to O, then the next point encountered is N, and finally G, leading back to S. The segments, therefore, are also in order; SO, ON, NG, and GS. Angles O and G oppose each other, but so do S and N; what gives it away is that sides NO (or ON, if you prefer) and GS are also opposite each other since they share no endpoints. 

This mentioning of vertices and sides in order will be important when proving polygons to be congruent because of the principle of CPCTC--"Corresponding Parts of Congruent Triangles are Congruent". How you mention the polygons will tell which angle in the first triangle corresponds to which one in the second.
The answer is NO and GS, angle O and angle G

Answerthe simplified expression isexplanationthe given expression is,let us deal with the bracket first.the two negatives in the parenthesis will become positive.the expression now becomes,we now expand the parenthesis to get,we group like terms to obtain,this simplifies to,