# Right triangle

(*) New you can now enter angles in different units: degree, percentage, radian and multiple of pi radian. To enter pi/6 angle, enter `\alpha` = 1/6 and choose from the units drop-down list "× pi radians".

## Right triangle formulas

### Pythagorean theorem

In a right triangle, the square of the hypotenus is equal to the sum of squares of the other two sides.`c^2 = a^2+b^2`

The converse is also true. For a given triangle, if the square of the longest side is equal to the sum of squares of the other two sides then this triangle is right-angled.

### Trigonometric ratios in a right triangle

`sin(\alpha) = b / c` ; `cos(\alpha) = a / c``tan(\alpha) = b / a` ; `cot(\alpha) = a / b`

Less used ratios are secant (sec) and cosecant (csc).

`sec(\alpha) = c / a = 1/cos(\alpha)` ; `csc(\alpha) = c / b = 1/sin(\alpha)`

In other words,

sine = opposite side / hypotenuse

cosine = adjacent side / hypotenuse

tangent = opposite side / adjacent side

cotangent = adjacent side / opposite side

And for less used ratios,

secant = hypotenuse / adjacent side

cosecant = hypotenuse / opposite side

### Complementary angles

In a right triangle, the acute angles `\alpha` and `\beta` are complementary because the sum of the three angles is 180 degrees and the third (right) angle is 90 degrees. So,`\alpha + \beta = 90°`

### Perimeter and area

The perimeter of a triangle is simply equal to the sum of its three sides.`P = a+b+c`

The area of the right triangle is equal to, `A = (a*b)/2`

### Right triangle altitude theorem

h : altitude (or height) on the hypotenusep : projection of leg a on the hypotenuse

q : projection of leg b on the hypotenuse

The square of the altitude on the hypotenuse is equal to the geometric mean of the projections of the legs (non-hypotenuse sides) on the hypotenuse.

`h^2 = p*q`

### Leg geometric mean Theorem or Leg rule

The length of a leg of a right triangle is the geometric mean of the lengths of the hypotenuse and the projection of that leg on the hypotenuse.`a^2 = p*c <=> a = sqrt(p*c)`

`b^2 = q*c <=> b = sqrt(q*c)`

## See also

Plane Geometry calculators

Geometry calculators

Mathematics calculators