Question

calculati:a)1+2+3....+56+57+58;b)1+2+3+....+35+36+37;c)2+4+6+.....+86+88+90;d)1+5+10+15+...+65+70

Answer 1

a) S = 1+2+3....+56+57+58 = (58*59)/2 = 1711

b) S = 1+2+3+....+35+36+37 = (37*38)/2 = 703

c) S = 2+4+6+.....+86+88+90 = 2(1+2+3+...+45) = 2* (45*46)/2 = 2070

d) S = 1 + 5+10+15+...+65+70 = 1 + 5(1+2+3...+14) = 1 + 5 * (14*15)/2 = 1 + 455 = 456