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1. Use the Pascal's identity to write an expression of the form (") that is equivalent to each of the following. a) () + () = b) (1 1 ) + ("1 1 ) = 2. Write the terms in the expansion of the following. Do not simplify your answer. (atb)' = 3. In the expansion of (x + y) , write the value of the exponent k in the term that contains a) xky8 b) xky+k 4. Using the arrangements of letters to the right, M compute the number of paths that spell the word MATH if all paths must start at the top and move diagonally down A A through the letters. T T T H H H H