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A ladder rests against a wall. One angle. Three sides. Six ratios.

Chapter 8 is Introduction to Trigonometry. It names the ratios of a right triangle. It proves one identity about them. An identity is an equation true for every acute angle.

What this track covers

• Naming the sides — opposite, adjacent and hypotenuse for one angle.
• Three ratios and their flips — sin, cos, tan and cosec, sec, cot. A flip is 1 divided by the ratio.
• The angle owns the ratio — same angle, same ratio, any size.
• The exact values — for 0°, 30°, 45°, 60° and 90°. Exact means not rounded.
• One identity — sin²A + cos²A = 1, and two more that follow.

Quick catch-up

• A ratio is one number divided by another.
• The hypotenuse is the side across from the right angle.
• In a right triangle, a² + b² = c². Here c is the hypotenuse.
• A right angle is exactly 90°.
• An acute angle is smaller than 90°.
• An equilateral triangle has three equal sides and three 60° angles.

Open the chapter. Read every exercise as a triangle to name.