Slide50.JPG

Slide51.JPG
Slide52.JPG Slide53.JPG

Learn in your speed, with individual attention - Teachoo Maths 1-on-1 Class


Transcript

Example 17 (Method 1) If nC9 = nC8, find nC17 . nC9 = nC8 𝑛!/9!(𝑛 − 9)! = 𝑛!/(𝑛 − 8)!8! 𝑛!(𝑛 − 8)!/(𝑛 − 9)!𝑛! = (9! )/8! (𝑛 − 8)!/((𝑛 − 9)! ) = (9! )/8! ((𝑛 − 8)(𝑛 − 8 − 1)!)/((𝑛 − 9)! ) = (9 × 8! )/8! ((𝑛 − 8)(𝑛 − 9)!)/((𝑛 − 9)! ) = 9 n – 8 = 9 n = 17 nCr = 𝑛!/𝑟!(𝑛 − 𝑟)! Now we have to find nC17 Putting n = 17 = 17C17 = 17!/17!(17 − 17)! = 17!/(17! × 0!) = 17!/(17! × 1) = 1/1 = 1 Example, 17 (Alternative Method) If nC9 = nC8, find nC17 . Given nC9 = 4C8 If nCp = nCq then either p = q or p + q = n p = q 9 = 8 Which is not possible p + q = n 9 + 8 = n n = 17 Now we have to find nC17 Putting n = 17 = 17C17 = 17!/17!(17 − 17)! = 17!/(17! × 0!) = 17!/(17! × 1) = 1/1 = 1

Ask a doubt
Davneet Singh's photo - Co-founder, Teachoo

Made by

Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.