P(m): 1+5+9+...+(4n-3)=n(2n-1); n∈N*
1)P(1): 1=1(2-1)
1=1 (A)
2)Sa presupunem ca P(k)-"A"∨k∈N* . Se demonstreaza ca P(k+1) este adevarat.
P(k): 1+5+9+...+(4k-3)=k(2k-1)
P(k+1): 1+5+9+...+(4k-3)+ (4k+1)=(k+1)(2k+1)
k(2k-1) + (4k+1)=(k+1)(2k+1)
2k²-k+4k+1=2k²+k+2k+1
2k²+3k+1= 2k²+3k+1- "A"⇒ P(k)-"A"⇒ P(n)-"A"