Find the 12th term of the geometric sequence 1, –4, 16,​

⇒ common ratio =r=3 and the given sequence is geometric sequence. Where an is the nth term, a is the first term and n is the number of terms. ⇒ 12th term is 708588 .

(May be wrong for some other users, although it's correct for me.)

geometry: triangles

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call the larger triangle abc

then the smaller triangle cde is similar to abc (all angles are equal, aaa).  

ab is the side that is 36, and we wish to find de, the side corresponding to ab

area_cde = area_abc - area_cde --> area_abc / area_cde = 2

let x=length of de

ratio of areas = (ratio of sides)^2

+2+=+%2836%2fx%29%5e2+

+2+=+1296%2fx%5e2+

++x%5e2+=+1296%2f2+=+648+

25.45584