Решение третьей задачи. Принцип Дюамеля. Полная формула Киргофа

u(x, t) = ν(x, t, τ)dτ = (t − τ)f(x + a(t − τ)ξ, τ)dS_ξdτ
	Δu = Δν(x, t, τ)dτ u_t = ν_t(x, t, τ)dτ + ν(x, t, t) = ν_t(x, t, τ)dτ
u_tt = ν_tt(x, t, τ)dτ + ν_t(x, t, t) = ν_t(x, t, τ)dτ + f(x, t)
u_tt − a²Δu = (ν_tt − a²Δu)(x, t, τ)dτ + f(x, t) = f(x, t)

u(x, t) = ν(x, t, τ)dτ, u_t(x, t) = ν_t(x, t, τ)dτ

u(x, 0) = ν(x, 0, τ)dτ = 0, u_t(x, 0) = ν_t(x, 0, τ)dτ = 0

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