The doctrine of triangles a history of modern trigonometry حسب Van Brummelen, Glen

Available for University of the Philippines Diliman via IEEE Xplore. Click here to access
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Schaum's outline of precalculus حسب Safier, Fred

Available for University of the Philippines Diliman via McGraw-Hill Access Engineering. Click here to access
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Three-way journal writing effects on students' problem-solving and self-regulation skills in trigonometry حسب Lugtu, Ivy C.

Precalculus functions and graphs حسب Swokowski, Earl William 1926-, Cole, Jeffery A. 1955-

Schaum's outline of trigonometry حسب Moyer, Robert, Ayres, Frank 1901-1994

Available for University of the Philippines Diliman via McGraw-Hill Access Engineering. Click here to access
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The fractional trigonometry with applications to fractional differential equations and science حسب Lorenzo, Carl F., Hartley, Tom T.

A basic approach to precalculus trigonometry preparing to succeed in calculus حسب Kim, Young H., Kim, Youngsoo, Tameru, Ana, Yan, Wen

Plane & spherical trigonomerty a tetrahedron approach حسب Mamhot, Millard R., Endam, Joemar C., Mamhot, Alice A., Banagua, Emelyn C., Bantug, Jenette S.

Worktext in college trigonometry حسب Domingo, Alleli C., Dimasuay, Lynie B., Lawas, Vernel M., Lubag, Sharon P., Almonte, Velimor D.

Plane & spherical trigonometry a tetrahedron approach حسب Mamhot, Millard R., Endam, Joemar C., Mamhot, Alice A., Banagua, Emelyn C., Bantug, Jenette S.