DescriptionTrigSumFormula.svg	Diagram for proof of trigonometric sum formula.
Date	7 September 2008
Source	Own work based on: TrigSumFormula.png by Liftarn
Author	Original: Liftarn   Vector: Edudobay using Eukleides.
SVG development InfoField	The SVG code is valid.  This trigonometry was created with Inkscape.

box(-0.15, -0.15, 1.1, 1.1, 4.5);

O = point(0, 0);
x_axis = line(O, 0<);
l_alpha = line(O, 24:);
l_beta = line(O, 60:);

P = point(l_beta, 1);
PQ = perpendicular(l_alpha, P);
Q = intersection(l_alpha, PQ);

QA = perpendicular(x_axis, Q);
A = intersection(x_axis, QA);

PB = perpendicular(x_axis, P);
B = intersection(x_axis, PB);

QR = parallel(x_axis, Q);
R = intersection(PB, QR);

mark(R,P,Q, simple, 0.3); % alpha
mark(B,O,Q, simple, 0.3); % alpha
mark(Q,O,P, simple, 0.25); % beta
mark(point(l_alpha, 2),Q,P, dotted, 0.2);

draw("$O$", O, .03, 220:);
draw("$P$", P, .03, 124:);
draw("$Q$", Q, .03, -34:);
draw("$R$", R, .03, 180:);
draw("$A$", A, .03, -90:);
draw("$B$", B, .03, -90:);

draw("$\alpha$", P, .18, -78:);
draw("$\alpha$", O, .17, 12:);
draw("$\beta$", O, .15, 42:);

draw(segment(P,Q));
draw(segment(Q,R));
draw(segment(P,B));
draw(segment(Q,A));
draw(segment(O, point(x_axis, 1.0)));
draw(segment(O, point(l_alpha, 1.1)));
draw(segment(O, point(l_beta, 1.2)));

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