Question

3+6+9.+.........+2019.calculati .stiind ca ..a+b=15 si x*a+x*b+3x=432

Answer 1

Salut!:)

1 ) 3 + 6 + 9 + .... + 2019

3 ( 1 + 2 + 3 + ... + 673 )

1 + 2 + 3 + ... + 673 --> Suma gauss

Suma Gauss :

S = 1 + 2 + 3 + ... + n

S = n ( n + 1 ) / 2

1 + 2 + 3 + ... + 673 = 673 × 674 / 2 = 337 × 673 =226 801 3 × 226 801 = 680 403

2) x = ?

a + b = 15

x ×

x = 24

2 )x = ?

a + b = 15

a + x × b + 3 x =432

x ( a + b ) + 3x = 432

15x + 3x = 432

18x = 432

x = 24

Bafta!:)