How many ways can 4 people sit at a table with 6 seats

In the following diagram it is given that dec,ab || dc, ad || eb, and ad is congruent to bc. a)why isn't abc a parallelogram even though it has a pair of parallel sides and a pair of congruent sides b)explain why be must be congruent to bc. further explain what type of triangle this makes triangle abc and what it tells you about angle 1 and angle 2c) finally why must angle 3 be congruent to angle 1? further, explain why we know that angle 3 is congruent to angle 2

Look at this pattern ; 1,4,9, number 10000 belongs in this pattern . what’s the place of this number?

Write the sine and cosine values of a, b, respectively, in the figure for (1) and (2) + explanation.