Question

Calculați sumele:

[\large S1 =10+11+12+.....+50]

[\large S2 =1+3+5+7+.....+99]

[\large S3=2+4+6+.......+100]

Answer 1

 a)
 
S=10+11+12+,,,,,,,,,+50=(50*51)/2=2550/2=1275

b)

S=1+3+5+7+..........+99=n*n
S=1+3+5+7+..........+2n-1=
99=2n-1⇒2n=99+1
                   n=100/2=50
S=1+3+5+7+.......+99=50*50=2500
 
C)

S=2+4+6+.......+100=n*(n+1)
S=2+4+6+.......+2n=
2n=100⇒n=50⇒n+1=51
S=2+4+6+.....+100=50*51=2550