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2011 1 .
44 3,666 ICP110745ICP13052560-1 11010802020088 11220250001 [2025]0422-132 .
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\[ S_n = a \frac{r^n - 1}{r - 1} \]
\( a = 3, r = 2, n = 8 \)
\[ S_8 = 3 \frac{2^8 - 1}{2 - 1} = 3(256 - 1) = 3 \times 255 = 765 \]
8th term:
\[ a_8 = ar^{7} = 3 \times 128 = 384 \]
Sum: 765, 8th term: 384
#### 384
A rectangle has length \( x + 5 \) and width \( x - 3 \). If the area is 120 square meters, find the positive value of \( x \), then compute the perimeter.
\[ (x + 5)(x - 3) = 120 \]
\[ x^2 + 2x - 15 = 120 \]