SF Calculator

Sequences + formulas (working).

Choose a calculation

Pick a tool, fill the inputs, then calculate.

Result
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Triangle Calculator

Right triangle solver: enter angle α + one side → get unknown side(s).

Solve right triangle (sin / cos / tan / cot)

Angle is α in degrees. Triangle must be right-angled.

Use 0 < α < 90
Side is relative to angle α
Side is relative to angle α
In “Two Sides → Angle” mode, this section is ignored.
Result
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Formulas used
sin(α)=opp/hyp, cos(α)=adj/hyp, tan(α)=opp/adj, cot(α)=adj/opp

Circle Calculator

Purple advanced circle tools: circumference, area, radius, arc, sector, chord, and segment.

Choose a circle calculation

Pick a formula, enter the known values, then calculate.

Result
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Core formulas
C = 2πr = πd, A = πr², L = (θ/360)·2πr, sector area = (θ/360)·πr², chord = 2r·sin(θ/2)

Tools

Use the formula helper on the left and convert units on the right.

Formula Helper

Type expressions like \pi*5^2, \sqrt(49), sin(30), 3/4

Shortcuts: \pi, \sqrt(...), sin(...), cos(...), tan(...), ^
Pretty Preview
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Result
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Unit Converter

Convert metric and common imperial units.

Result
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How it was converted
Click Convert to see the base-unit method and answer.

Notes

Scroll down to read more. Each topic has its own color tone.

Search filters topics instantly.

Angles

  • Acute: 0° < x < 90°
  • Right: x = 90°
  • Obtuse: 90° < x < 180°
  • Straight: x = 180°
  • Reflex: 180° < x < 360°
  • Convex: 0° < x < 180°
  • Concave / reflex: 180° < x < 360°

Triangles

  • Acute triangle: all angles < 90°
  • Right triangle: one angle = 90°
  • Obtuse triangle: one angle > 90°
  • Equilateral: all sides equal (all angles 60°)
  • Isosceles: two sides equal (two base angles equal)

Right-triangle Trigonometry

  • sin(α) = opposite / hypotenuse
  • cos(α) = adjacent / hypotenuse
  • tan(α) = opposite / adjacent
  • cot(α) = adjacent / opposite

Circles

  • Radius: r = d / 2
  • Diameter: d = 2r
  • Circumference: C = 2πr = πd
  • Area: A = πr²
  • Radius from circumference: r = C / (2π)
  • Radius from area: r = √(A / π)
  • Arc length: L = (θ / 360) · 2πr
  • Sector area: A = (θ / 360) · πr²
  • Chord length: c = 2r sin(θ / 2)
  • Segment area: (θ / 360)πr² − ½r²sin(θ)
  • Sector perimeter: P = 2r + L
  • Important: use degrees in the formula, but convert to radians for JavaScript trig functions.

Parallel Lines & Angles

  • Vertically opposite angles are equal.
  • Corresponding angles are equal (if lines are parallel).
  • Alternate angles are equal (if lines are parallel).
  • Angles on a straight line add to 180°.