Prove: quadrilateral abcd is a parallelogram.
reason
proof:
statement
1. ac and bd bisect each other.
2. ae = ec
be= ed
3. m_aeb = m_ced
4. aabe acde
given
definition of bisection
sas criterion
5. lacd xl cab
corresponding angles of congruent
i triangles are congruent.
what is the reason for step 3 of this proof?
a. alternate interior angles theorem
b. corresponding angles in congruent triangles are congruent.
c. for parallel lines cut by a transversal, corresponding angles are congruent.
d. vertical angles theorem
e. sas criterion for congruence

Suppose we have a set of small wooden blocks showing the 26 letters of the english alphabet, one letter per block. (think of scrabble tiles.) our set includes 10 copies of each letter. we place them into a bag and draw out one block at a time. (a) if we line up the letters on a rack as we draw them, how different ways coukl we fill a rack of 5 letters? (b) now suppose we just toss our chosen blocks into a pile, and whenever we draw a letter we already have, we put it back in the bag and draw again. how many different piles of 5 blocks could result? possible? piles will contain at least one repeated letter? (c) if we draw out 5 blocks wit hout looking at them, how many different piles are (d) if we draw out 5 blocks without looking at them, how many of the possible 2. (4) consider the following formula. 12 give two different proofs, one using the factorial formulas and the other combina torial.