Odpowiedzi

2009-11-20T03:45:35+01:00
A₃ = 10
a₇ = 42

a₁ = ?
r = ?

an = a₁+(n-1)*r

a₃ = a₁ + (3-1)*r = 10
a₇ = a₁ + (7-1)*r = 42

a₁ + 2r = 10
a₁ + 6r = 42


a₁ = 10 - 2r
10-2r + 6r = 42


a₁ = 10 - 2r
4r = 42-10

a₁ = 10 - 2r
4r = 32

a₁ = 10 - 2r
r = 8

a₁ = 10 - 2*8
r =8

a₁ = 10 -16 = 4
r = 8

a₁ = 4
r = 8