Question Number 10290 by konen last updated on 02/Feb/17

3×3!+4×4!+...+12×12!=?

Answered by ridwan balatif last updated on 02/Feb/17

3×3!+4×4!+...+12×12!  (4−1)×3!+(5−1)×4!+(6−1)×5!+...+(13−1)×12!  4×3!−1×3!+5×4!−1×4!+6×5!−1×5!+...+13×12!−1×12!  4!−3!+5!−4!+6!−5!+...+13!−12!  −3!+13!  13!−3!