The best replacement for trigonometry is precalculus.

The best alternatives to trigonometry are rated as following:
★★★★★  precalculus
★★★★  calculus
★★★  geometry
★★★  statistics
★★★  algebra
★  college algebra
★  calculus first
★  statistics harder
★  precalculus first
  calculus harder
  pre calculus
  algebra 2
  college algebra harder
  pre calc
  finite math
  algebra 3

Your alternative for trigonometry is not listed? Suggest!
Speaking about trigonometry, one probably shouldn't forget about analytic geometry.

Other search terms related to trigonometry and their ratings are:
★★★★★ analytic geometry
★★★★ triangles
★★★★ right triangles
★★★ vectors
★★★ geometry
★★ right angles
★ complex numbers
★ algebra
knowing algebra
bearings
non right angled triangles
You have in mind a companion for trigonometry and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of trigonometry in all years. Click on graph for more.
trigonometry
precalculus
calculus