Please help me understand this!!

Step-by-step explanation:

3 + 15 + 75 + 375 + 1,875

This is a geometric series.  The first term is 3, the common ratio is 5, and the number of terms is 5.

∑₁⁵ 3 (5)ⁿ⁻¹

∑₀⁴ 3 (5)ⁿ

3 + 12 + 48 + 192 + 768

This is a geometric series.  The first term is 3, the common ratio is 4, and the number of terms is 5.

∑₁⁵ 3 (4)ⁿ⁻¹

∑₀⁴ 3 (4)ⁿ

4 + 32 + 256 + 2048 + 16,384

This is a geometric series.  The first term is 4, the common ratio is 8, and the number of terms is 5.

∑₁⁵ 4 (8)ⁿ⁻¹

∑₀⁴ 4 (8)ⁿ

2 + 6 + 18 + 54 + 162

This is a geometric series.  The first term is 2, the common ratio is 3, and the number of terms is 5.

∑₁⁵ 2 (3)ⁿ⁻¹

∑₀⁴ 2 (3)ⁿ

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step-by-step explanation:

(3x-8) or (3x+8)

step-by-step explanation: