ответ: а₅₀ = 100, S₅₀ = 2550.
1). a₅₀ = a₁ + 49d
a₅₀ = 2 + 49*2 = 2 + 98 = 100.
2). S₅₀ = (a₁ + a₅₀)*50/2
S₅₀ = (2 + 100)*50/2 = 102*50/2 = 2550.
