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

Available for University of the Philippines Diliman via IEEE Xplore. Click here to access
Also available remotely for University of the Philippines Diliman via IEEE Xplore. Click here to access thru EZproxy

Schaum's outline of precalculus by Safier, Fred

Available for University of the Philippines Diliman via McGraw-Hill Access Engineering. Click here to access
Also available remotely for University of the Philippines Diliman via McGraw-Hill Access Engineering. Click here to access thru EZproxy

Three-way journal writing effects on students' problem-solving and self-regulation skills in trigonometry by Lugtu, Ivy C.

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

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

Available for University of the Philippines Diliman via McGraw-Hill Access Engineering. Click here to access
Also available remotely for University of the Philippines Diliman via McGraw-Hill Access Engineering. Click here to access thru EZproxy

The fractional trigonometry with applications to fractional differential equations and science by Lorenzo, Carl F., Hartley, Tom T.

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

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

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

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