Discrete Structures Example of number 3 and 4 I want in same

Discrete Structures

Example of number 3 and 4. I want in same format or similar

Example of number 5. I want in same format or similar

let n=odd=2k+1,k E z

sustituting n value in the given equation

((2k+1)^2)/2=(((2k+1)^2)-1)/2

next multipilying

(4k^2 +4k+1)/2=(4k^2 +4k+1-1)/2

by division with 1/4

k^2+k+1/4=k^2+k

LHS NOT EQUAL TO RHS