Solve the following equality : cos2v=cos40

Take the inverse cosine of both sides.

... arccos(cos(2v)) = arccos(cos(40°))

... 2v = ±40° + k·360° . . . . . for k = any integer

... v = ±20° + k·180° . . . . . . for k = any integer

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

answer: 10 turtles

step-by-step explanation: as turtles have four legs so 4.10=40 therefore birds are 4 which sue counted