Question

Calculați:
a) 1 supra 13+2 supra 13+3 supra 13+...+51 supra 13
b) 1 supra 40+3 supra 40+5 supra 40+...+79 supra 40
c) 2 supra 9+4 supra 6+6 supra 9+...+142 supra 9
d) 3 supra 19+7 supra 19+11 supra 19+...+1595 supra 19

Answer 1

a) (1+2+...+51)/13=(51*52/2)/13=1326/13=102
b) (2*1-1+2*2-1+2*3-1+...+2*40-1)/40=2*(40*41/2)-40)/40=(40*41-40)/40=40*40/40=40
d)(4*1-1+4*2-1+4*3-1+...+4*399-1)/19=(4*(399*400/2)-399)/19=399*400*2/19=319300/19=16800

Answer 2

5 rad 2
5 rad 3
12 rad 5
3rad 14
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