Why the Unit Circle?

Why do we use a unit circle when talking about trigonometry?

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Why do we use a “unit circle”?

B = (0.5, -0.5)
p = Function({2.789495548265341, 4.71197879436495, 0.33620296344249284, 0.33620296344249284, 0.33620296344249284, 0.33620296344249284, 0.33620296344249284, 0.33620296344249284, 0.33620296344249284, 0.33620296344249284, 0.33620296344249284, 0.33620296344249284, 0.33620296344249284, 0.33620296344249284, 0.33620296344249284, 0.33620296344249284, 0.3342995146839784, 0.33239606592546395, 0.33049261716694944, 0.328589168408435, 0.32668571964992055, 0.32668571964992055, 0.32668571964992055, 0.32668571964992055, 0.32668571964992055, 0.32668571964992055, 0.32668571964992055, 0.32668571964992055, 0.32668571964992055, 0.32668571964992055, 0.32509951235115847, 0.32351330505239645, 0.32192709775363443, 0.32192709775363443, 0.32192709775363443, 0.32192709775363443, 0.32192709775363443, 0.32192709775363443, 0.32192709775363443, 0.32192709775363443, 0.32192709775363443, 0.32192709775363443, 0.32351330505239645, 0.32509951235115847, 0.32668571964992055, 0.3282719269486826, 0.32985813424744465, 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2.2301344781643753, 2.2301344781643753, 2.2301344781643753, 2.2301344781643753, 2.2333068927618993, 2.2364793073594234, 2.2396517219569474, 2.2396517219569474, 2.2396517219569474, 2.2396517219569474})
J = Point(p)
I = Point(p)
j: x(J) - x(I)
i: y(J) - y(I)
t = 1 (slider from 0 to 1, step 0.001)
K: (x(I) + (t * j), p(x(I) + (t * j)))
mover: (y(K) - y(I)) / i
O = Intersect(xAxis, yAxis)
a = Line(O, B)
c = Circle(O, 1)
C = Intersect(c, a, 1)
u = Vector(B, C)
A = (2, 1)
b = Line(O, A)
D = Intersect(c, b, 1)
v = Vector(A, D)
d = Segment(C, B)
e = Segment(D, A)
E: B + (mover * u)
f = OrthogonalLine(E, xAxis)
F: A + (mover * v)
g = OrthogonalLine(F, xAxis)
G = Intersect(f, xAxis)
H = Intersect(g, xAxis)
poly1, g_1, o, e_1 = Polygon(O, E, G)
poly2, h, o_1, f_1 = Polygon(O, F, H)
k = OrthogonalLine(A, xAxis)
l = OrthogonalLine(B, xAxis)
L = Intersect(l, xAxis)
M = Intersect(k, xAxis)
poly3, a_1, o_2, m = Polygon(O, M, A)
poly4, l_1, o_3, b_1 = Polygon(O, B, L)