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

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

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

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

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

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

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

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