Right-Triangle Trigonometry
Aligned to G-SRT.C.8 — Common Core State Standards for Mathematics.
What this lesson teaches
In a right triangle, sine, cosine, and tangent relate an angle to ratios of sides (SOH-CAH-TOA). Use them to find missing sides or angles.
Worked example
To find the side opposite a 30° angle when the hypotenuse is 10: sin(30°) = opposite/10, so opposite = 10 × 0.5 = 5.
Practice questions
- Write the ratio for tangent of an angle.
- Find the opposite side if sin(40°)≈0.64 and hypotenuse = 20.
- What does SOH-CAH-TOA help you remember?
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Trigonometría en triángulos rectángulos
En un triángulo rectángulo, el seno, el coseno y la tangente relacionan un ángulo con razones entre los lados (SOH-CAH-TOA). Úsalos para encontrar lados o ángulos desconocidos.
Ejemplo: Para encontrar el lado opuesto a un ángulo de 30° cuando la hipotenusa mide 10: sin(30°) = opuesto/10, entonces opuesto = 10 × 0.5 = 5.
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