Question

ajutatima si pe mine va rog

1)4+8+12+...+400=

2)8+16+24+...+3200=

3)10+20+30+...+480=

Answer 1

Răspuns: Facem suma lui gauss.Formula este nx(n+1):2 ; n este ultimul numar din sir.

• 4+8+12+...+400=4x(1+2+3+.....+100)=4x[100x(100+1):2]=4x5050=20200
• 8+16+24+.......3200=8x(1+2+3+.....+400)=8x[400x(400+1):2]=8x80200=641600
• 10+20+30+.....+480=10x(1+2+3+.......48)=10x[48x(48+1):2]=10x1176=11760

   Sper ca te-am ajutat! <3

Answer 2

Explicație pas cu pas:

1)4×1+4×2+4×3+...+4×100=

4×(1+2+3+...+100)=

4×[n×(n+1)]:2=

4×(100×101):2=

4×10 100:2=

4×5050=20 200

2)8×1+8×2+8×3...+8×400=

8×(1+2+3+...+400)=

8×[n×(n+1)]=

8×(400×401):2=

8×160 400:2=

8×80 200=641 600

3)10×1+10×2+10×3+...+10×48=

10×[n×(n+1)]=

10×(48×49):2=

10×2352:2=

10×1176=11 760