A few sides and angles let you find area, and even height
Trig ratios let you calculate area or height without ever measuring a shape directly. Know just two sides and the angle between them, and you can find a triangle's area; know just an angle of elevation and a distance, and you can find the height of a building you can't measure by eye.
Set two sides a, b and the included angle C between them, and the triangle is completely determined. Without ever measuring a base and height directly, the formula Area = (1/2)×a×b×sinC gives the area right away.
Side a6
Side b8
Included angle C60°
If you know the angle of elevation θ from which you look up at the top of a building from a spot some distance away, and the horizontal distance x to that spot, you can find the building's height without measuring it directly: height h = x × tanθ.