Question

4. Calculati sumele: a) S = 1 + 2 + 3 + ... + 20 b) S=2 + 4 + 6+ ... + 100 ​

Answer 1

a) S=1+2+3+...+20

S=20•21:2

S=10•21

S=210

b) S=2+4+6+...+100

S=2 + 4 + 6 +... + 100

S=100+96+94+...+2

———————————,,+"

2•S=102+102+102+...+102

2•S=102 •nr. term.

2•S=102•50

S=102•50:2

S=51•50

S=2 550

nr. term:(ult.-prim.):pas+1

=(100-2):2+1

=98:2+1

=49+1

=50

Cu plăcere!!!