A flight of stairs has 9 steps. Alice can go up for 1 step or 3 steps each time. How many
ways are there for Alice to go up the stairs?
How to do that?

Tính nhanh:

\(\left(-2\right)+7+\left(-12\right)+17+...+\left(-52\right)+57\)

Giải hộ mình với ak!

Tính nhanh:

13 - 12 + 11 + 10 - 9 + 8 - 7 - 6 + 5 - 4 + 3 + 2 - 1