Respuesta :

A1 = 7

An = 3A(n-1) + 4. According to this, A2 would be= 3*7 + 4 =25

A1 = 7, A2 = 25, then the difference is d = 18

The general formula for an aritmethic progression is An = A1 + (n -1)d

For A4 = 7 + (4-1)*18 = 61

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