25.1.4 Basic Relationships Among the Same Angle's Ratios
Core ideaThe three ratios of a single angle aren't strangers to each other: sin²A+cos²A=1 and tanA=sinA/cosA tie them all together.
Module goal. Carrying the function idea forward, we first build the link between an angle and the ratios of sides inside the most familiar shape — the right triangle — and learn to use it to measure real heights and distances.