Răspunsuri

2014-09-01T11:08:50+03:00
S=54+61 +68+....+2469

n=(2469-54):7+1

n=2415:7+1

n=345+1

n=346 termeni

S=(54+2469)*346/2

S= 2523*173

S=436 479

a_136= a_1 + ( 136-1)*7

a_136= 54+ 137*7

a_136= 54+ 959

a_136=1013

S=54+61+68+....+1013

S=(54+1013)*136/2

S=1067 *68

S=72 556