Trigonometry (also see 5.3)

Factoring Functions, J.C.Bodenrader, 2:1, 1971, 23-26, 5.1.2, 3.2, 9.1
An Interesting Correspondence and Its Consequence, Sidney Penner, 2:1, 1971,
40-44
Pascal's Triangle, Karl J. Smith, 4:1, 1973, 1-13, 3.2, 9.2
A "Doodling" Inequality, Benjamin Greenberg, 4:1, 1973, 78-79, C
A Classroom Theorem on Trigonometric Irrationalities, Norman Schaumberger, 5:1,
1974, 73-76, C
Square Functions, Helmer Junghans, 5:2, 1974, 15-18, 0.7
A Set of Trigonometric Inequalities with Applications to Maxima and Minima,
Norman Schaumberger, 5:3, 1974, 26-30, 5.1.4
A Generator of Trigonometric Identities, Aron Pinker, 5:4, 1974, 54-55, C
Mathematical Astronomy, Vincent J. Motto, 6:1, 1975, 21-26
Closing the Loopholes, Morton Bloomfield and Frank Lasak, 6:2, 1975, 42-44, C
An Interesting Use of Generating Functions, Aron Pinker, 6:4, 1975, 39-45,
5.4.2, 9.5
Closing the Loopholes in "Closing the Loopholes", Gene Zirkel, 7:3, 1976,
55-58, C
Another Note on "Closing the Loopholes", Larry F. Bennett, 7:3, 1976, 56-58, C
Quasi-Pythagorean Triples for an Oblique Triangle, Kay Dundas, 8:3, 1977,
152-155, 9.3
Geometric Proofs of the Formulas for Sin(x+y) and Cos(x+y), Norman
Schaumberger, 10:1, 1979, 35, C
An Ellipse Problem Beyond the Reach of Calculus, Ivan Niven, 10:3, 1979,
162-168, 0.5
Why Can't We Trisect an Angle This Way?, David Beran, 10:3, 1979, 199-200, C
Products of Sines, Zalman Usiskin, 10:5, 1979, 334-340
Geometric Interpretations of Sin(phi1)+Sin(phi2)=1, Charles Muses, 10:5, 1979,
350-351, C
A Formula for Sin (A+B), Simon J. Lawrence, 11:2, 1980, 125-126, C
Formulas for sin(x+y) and cos(x+y), Robert Geist, 11:2, 1980, 126, C
Trigonometric Solutions to the Quadratic Equation, Leo Chosid, 11:5, 1980,
330-331, C
A Coordinate Geometry Evaluation of ABS(tan(A-B)), Norman Schaumberger, 12:1,
1981, 52-54, C
Applying Complex Arithmetic, Herbert L. Holden, 12:3, 1981, 190-194, 5.3.1,
9.3, 9.5
Visual Application of Sin(theta1 + theta2) = Sin(theta1)Cos(theta2) +
Cos(theta1)Sin(theta2), Gerald E. Gannon, 12:3, 1981, 206, C
Sum Formulas for Sine and Cosine, Dan Kalman, 14:1, 1983, 55-56, C
The Steiner-Lehmus Theorem as a Challenge Problem, Ken Seydel and Carl Newman,
14:1, 1983, 72-75, 0.4
Approximation to an Angle Trisection, Glen Peterson, 14:2, 1983, 166-167, C
Integer-Sided Triangles with One Angle Twice Another, R.S.Luthar, 15:1, 1984,
5-56, C, 9.3
Proving Heron's Formula Tangentially, David E. Dobbs, 15:3, 1984, 252-253, C,
0.4
Approximate Angle Trisection, David Gauld, 15:5, 1984, 420-422, C, 5.4.2
Generalized Pythagorean Triples, W.J.Hildebrand, 16:1, 1985, 48-52, 5.5, 9.3
Pitfalls in Graphical Computation, or Why a Single Graph Isn't Enough, Franklin
Demana and Bert K. Waits, 19:2, 1988, 177-183, 5.1.5
The Fundamental Periods of Sums of Periodic Functions, James Caveny and Warren
Page, 20:1, 1989, 32-41, 9.5
The Double-Angles Formulas, Roger B. Nelsen, 20:1, 1989, 51, C
Lattices of Trigonometric Identities, Willeam E. Rosenthal, 20:3, 1989,
232-234, C, 5.2.3
Where There is Pattern, There is Significance, Lloyd Olson, 20:4, 1989, 321, C
FFF #11. A New Trigonometric Identity, Ed Barbeau, 20:5, 1989, 404, F (also
22:2, 1991, 132-133)
(Sin x)^2: A Sheep in Wolf's Clothing, Mark E. Saul, 21:1, 1990, 43-44, C,
5.1.5
FFF #18. Glide-Reflection to Sine Curve, Ed Barbeau, 21:3, 1990, 216, F
China's 1989 National College Entrance Examination, Bart Braden, 21:5, 1990,
390-393, 0.2, 0.4, 1.2
Trigonometric Identities through Calculus, Herb Silverman, 21:5, 1990, 403, C,
5.3.1
A Productive Error in a Trigonometry Text, Lee H. Minor, 22:4, 1991, 315-318, C
FFF #54. A Degree of Differentiation, Ed Barbeau, 23:3, 1992, 203, F, 5.1.3
(also 23:4, 1992, 306 and 24:4, 1993, 345)
FFF.  A 21-41-50 Triangle, Ed Barbeau, 23:4, 1992, 304, F
Cos(s-t) from the Distance Formula, Gilbert Strang, 23:4, 1992, 333, C
The Half-Angle Formula for Cotangent, Fen Chen, 23:5, 1992, C
The Half-Angle Formulas for the Tangent, Sidney H. Kung, 25:3, 1994, 205, C
A Simple Geometric Proof of the Addition Formula for the Sine, Jeffrey Li-chieh Ho, 25:3, 1994, 229-230, C
An Early Iterative Method for the Determination of Sine of One Degree, Farhad Riahi, 26:1, 1995, 16-21, 2.1
cos(x+y) (Proof Without Words), Sidney H. Kung, 26:2, 1995, 145, C
The Double-Angle Formulas via the Laws of Sines and Cosines, Sidney H. Kung, 27:2, 1996, 155, C
A Complex Approach to the Laws of Sines and Cosines, William V. Grounds, 27:2, 1996, 108, C, 9.5
A Law of Cosines (Proof Without Words), S. H. Kung and Jingcheng Tong, 27:3, 1996, 219, C
FFF #122. On Not Identifying Equations and Identities, Richard Askey, 28:5, 1997, 377-379, F
Trigonometric Identity: The Difference of Two Sines or Two Cosines (proof without words), Yukio Kubayashi, 29:2, 1998, 133, C
Trigonometric Identity: The Sum of Two Sines or Two Cosines (proof without words), Yukio Kubayashi, 29:2, 1998, 157, C
Undersampled Sine Waves, J. C. Derderian and Enriqueta Rodriguez-Carrington, 29:3, 1998, 213-218, 5.1.5
FFF #130. Forces with a Given Resultant, Don Curran, 29:4, 1998, 301-302, F
FFF #133. Identifying the Angle, K. R. S. Sastry, 29:5, 1998, 405-406, F
Proof Without Words: tan(a-b), Guanshen Ren, 30:3, 1999, 212, C
A Simple Geometric Solution to De l'Hospital's Pulley Problem, Raymond Boute, 30:4, 1999, 311-314, C, 0.3
Measuring the Curl of Paper, Joseph Paullet and Richard Bertram, 30:4, 1999, 315-317, C, 5.1.4
One Figure: Six Identities, Roger Nelsen, 31:2, 2000, 145-156, C