(a + b) 0 =1 (a + b) 1 = (a + b) 2 = (a + b) 3 = 1a 1 + 1b 1 1a 2 + 2ab + 1b 2 1a 3 + 3a 2 b + 3ab 2 + 1b 3 Binomial Expansion... What do we notice????
Pascal’s Triangle
Example Expand (a + b) 6 Solution: (a + b) 6 = a 6 + 6a 5 b + 15a 4 b a 3 b a 2 b 4 + 6ab 5 + b 6
Example Find the first four terms in the expansion of (x – 2y) 7. Solution (a + b) 7 = a 7 + 7a 6 b + 21a 5 b a 4 b 3 + ….. Substitute: x = a, 2y = b (x + 2y) 7 = x 7 + 7x 6 (2y) + 21x 5 (2y) x 4 (2y) Simplify (x + 2y) 7 = x x 6 y + 84x 5 y x 4 y 3
Example a a 11 b + 66a 10 b a 9 b 3
Factorial Notation r! = r(r-1)(r-2)(r-3)…..3*2*1 9! = 9*8*7*6*5*4*3*2*1 = ! = 12*11*10*9*8*7*6*5*4*3*2*1 = What happens when we divide factorials? Calculators can help! MATH -> PRB -> #4
Therefore, you can write the fourth term of the expansion of (a + b) 12 as follows: Please write a formula for the k term of the expansion of (a + b) n.
Example Find and simplify the seventh term in the expansion of (2x-y) (2x) 4 (-y) 6 = 210 * 16x 4 * y 6 = 3360x 4 y 6