Question

a) 15 + 16 + ... + 95 = ?
b) 49 + 50 + 51 + ... + 250 = ?
c) 24 + 26 + 28 + ... + 100 = ?
d) 20 + 25 + 30 + ... + 300 = ?
e) 19 + 21 + 23 + ... + 2019 = ?

Va rog mult, am nevoie urgenta!

Answer 1

a) 15 + 16 + ... + 95 =

= (1+2+3+...+95) - (1+2+3+...+14) =

= (95•96)/2 - (14•15)/2 =

= 95•48 - 7•15 =

= 4455

b) 49 + 50 + 51 + ... + 250 =

= (1+2+3+...+250) - (1+2+3+...+48) =

= (250•251)/2 - (48•49)/2 =

= 125•251 - 24•49 =

= 30199

c) 24 + 26 + 28 + ... + 100 =

= (2+4+6+...+100) - (2+4+6+...+24) =

= 2•(1+2+3+...+50) - 2•(1+2+4+...+12) =

= 2•(50•51)/2 - 2•(12•13)/2 =

= 50•51 - 12•13 =

= 2394

d) 20 + 25 + 30 + ... + 300 =

= 5•(4+5+6+...+60) =

= 5•[(1+2+3+...+60) - (1+2+3)] =

= 5•(60•61)/2 - 5•6 =

= 5•30•51 - 30 =

= 4620

e) 19 + 21 + 23 + ... + 2019 =

= (1+3+5+...+2019) - (1+3+5+...+17) =

= [(2019+1)/2]² - [(17+1)/2]² =

= 1008² - 9² =

= 1015983

Answer 2

Răspuns:

eu asa am facut la scoala sper ca te am ajutat

Explicație pas cu pas:

scuze ca am scris urat