3+6+9+12+....+99= 3( 1+2+3+..+33)
= 3 ×[tex] \frac{33*34}{2} [/tex]
=3×[tex] \frac{1122}{2} [/tex]
=3 ×561
=1683
4+8+12+16+....+100=4(1+2+3+..+25)
=4 × [tex] \frac{25*26}{2} [/tex]
= 4 ×[tex] \frac{650}{2} [/tex]
= 4 × 325
=1300
5+10+15+20+....+50=5(1+2+3+..+10)
= 5 ×[tex] \frac{10*11}{2} [/tex]
= 5 ×[tex] \frac{110}{2} [/tex]
= 5 × 55
=275
Baftă!
