Răspuns:
x = 291
Explicație pas cu pas:
4+8+12+16+...+864 = 3+6+9+12+...+720+24x <=>
4(1+2+3+4+....+216) = 3(1+2+3+....+240)+24x <=>
4(1+216)·216:2 = 3·(1+240)·240:2 + 24x =>
4·217·108 = 3·241·120 +24x =>
93744 = 86760 + 24x =>
24x = 93744-86760 =>
24x = 6984 =>
x = 6984:24 =>
x = 291
#copaceibrainly