Thomas R. answered • 03/30/19
Over 25 years of experience and a sense of humor about math
When are they not useful? You would need geometry for nearly any sort of project. If you want to halve or double a recipe, you will need geometry to calculate the size of your new saucepan or baking dish. You also need it for installing floor tiles, performing any sort of carpentry, and anything else that involves measuring in more than one direction at once.
Trigonometry was invented by early astronomers, but we use it daily without noticing it. Every road has a speed limit based on the friction between your tires and the road as well as the degree of curvature of the road. You need trig for carpentry also, as well as any sort of task involving calculating forces or movements. If you want to brace something, you need trig. If you want to lift or drag something? Trig. The military needs it for everything. A bullet, cannonball, missile or any other projectile will need trig. Even sports employ it, though it tends not to be conscious.
