Area
Rectangle: l·w. Triangle: (1/2)·b·h. Circle: πr². Trapezoid: (1/2)·(b₁+b₂)·h. Parallelogram: b·h.
Volume
Rectangular prism: l·w·h. Cube: s³. Cylinder: πr²·h. Sphere: (4/3)πr³ (rare on HSAT). Cone: (1/3)πr²·h.
Angles
Triangle interior angles sum to 180°. Quadrilateral: 360°. Polygon with n sides: (n−2)·180°. Each interior angle of a regular n-gon: (n−2)·180°/n.
Circles
Circumference: 2πr (or πd). Inscribed angle is half the central angle of the same arc. Area of sector: (θ/360)·πr².
Tip: revisit this strategy after every 10 missed questions on this topic.