Question

2 plus 6 plus 10 plus 14 plus trei puncte plus 30 egal doi ori x la puterea 3​

Answer 1

Răspuns:    x = 4

Explicație pas cu pas:

2 + 6 + 10 + 14 + ..... + 30 = 2 × x³

2×1 + 2×3 + 2×5 + 2×7 + ..... + 2×15 = 2 × x³

->  il dau factor comun pe 2

2 × ( 1 + 3 + 5 + 7 + ..... + 15 ) = 2 × x³   [  : 2

1 + 3 + 5 + ... + 15 = x³

( 15 - 1 ) : 2 + 1 = 14 : 2 + 1 = 8 termeni are suma cu ratia = 2

x³ = 8 × ( 1 + 15 ) : 2

x³ = 8 × 16 : 2

x³ = 2³ x 8

x³ = 2³ x 2³

x³ = ( 2 x 2 )³ =>   x = 4