x → ∞ lim x + x + x + x + ⋯ 3 x 3 x 3 x x = ?
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Why you say y>0?
It was an oral question. Just watch and answer.
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Let the limit be L and y = x + x + x + x + . . . 3 x 3 x 3 x ; ⟹ L = lim x → ∞ y x .
Now consider y as follows.
y = x + x + x + x + . . . 3 x 3 x 3 x = x + y 3 x
⟹ y 2 − x y − 3 x = 0 Solving the quadratic of y
⟹ y = 2 x + x 2 + 4 3 x Note that y > 0
Now, we have:
L = x → ∞ lim y x = x → ∞ lim 2 x + x 2 + 4 3 x x = x → ∞ lim x + x 2 + 4 3 x 2 x = x → ∞ lim 1 + 1 + x 5 / 3 4 2 = 1 + 1 + 0 2 = 1 Divide up and down by x