Topic explanation

Standard explanation

(n+1)! / n! = n+1. n! / (n-2)! = n(n-1) if n>=2. Never cancel inside n! as if it were n * !. Write the extra factors out.

Key points

• write extra factors
• n! = 12...*n
• 0! = 1
• 0! is 1
• CANCEL IN RATIOS: (n+1)! / n! = n+1. n! / (n-2)! = n(n-1) if n>=2. Never cancel inside n! as if it were n * !. Write t
• CANCEL IN RATIOS: (n+1)!
• WHAT — CANCEL IN RATIOS: (n+1)! / n! = n+1. n! / (n-2)! = n(n-1) if n>=2. Never cancel inside n! as if it were n * !. Write t
• WHY — Why it matters: This rule is a separate learning unit inside factorial n!. It can be defined, applied, and checked i

Labelled diagram