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

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Schaum's outline of precalculus od 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 od Lugtu, Ivy C.

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

Schaum's outline of trigonometry od 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 od Lorenzo, Carl F., Hartley, Tom T.

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

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

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

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