This page covers Trigonometry at the High School Introductory level, delivered as a formula cheat sheet. Sine, cosine, tangent — and the identities, laws, and unit circle that unlock calculus. The course w. The material here corresponds to Grades 9–10 courses: Algebra 1 and Geometry.
The key formulas for Trigonometry at the High School Introductory level are organised below. Each formula is accompanied by a note on when it applies and what common variations exist.
The skills covered by these formulas are: Unit circle, Right-triangle trigonometry, Trig identities, Law of sines and cosines, Inverse functions.
For each formula, read the conditions carefully. Many errors in Trigonometry come from applying a formula outside its domain of validity — using a geometric formula that assumes a right angle when the angle is not specified, or applying a probability rule that requires independence when the events are dependent.
Use this sheet as a revision tool after you have worked through problems — not as a first introduction to the material. A formula you have derived or used is one you will remember; a formula you have only read is one you will forget under exam pressure.
Worked Example
A standard trigonometry problem at the high school intro level.
Work through step by step: identify what is given, what is asked, apply the relevant technique, and check your answer against the original conditions.
Using degree values in radian-mode calculations (or vice versa) without checking the calculator mode.
Frequently Asked Questions
How is Trigonometry different at the HS Intro level compared to earlier levels?
At the High School Introductory level, Trigonometry builds on Grades 9–10 prerequisites. Students are expected to have completed Algebra 1 before tackling this material.
Which exams test Trigonometry at this level?
SAT Math (Level 2), ACT Math, AP Calculus BC.
What is the single most effective way to practise Trigonometry for HS Intro students?
The most effective practice at the High School Introductory level is deliberate work on novel problem setups — not repeated drilling of the same template. Attempt problems before looking at solutions, and review errors by identifying the specific step where the reasoning broke down.