# Right triangle calculator (a,b) - result

Please enter two properties of the right triangle

Use symbols: a, b, c, A, B, h, T, p, r, R

You have entered cathetus a and cathetus b.

### Right scalene triangle.

Sides: a = 12   b = 5   c = 13

Area: T = 30
Perimeter: p = 30
Semiperimeter: s = 15

Angle ∠ A = α = 67.3880135052° = 67°22'49″ = 1.17660052071 rad
Angle ∠ B = β = 22.6219864948° = 22°37'11″ = 0.39547911197 rad
Angle ∠ C = γ = 90° = 1.57107963268 rad

Height: ha = 5
Height: hb = 12
Height: hc = 4.61553846154

Median: ma = 7.81102496759
Median: mb = 12.25876506721
Median: mc = 6.5

Inradius: r = 2
Circumradius: R = 6.5

Vertex coordinates: A[13; 0] B[0; 0] C[11.07769230769; 4.61553846154]
Centroid: CG[8.02656410256; 1.53884615385]
Coordinates of the circumscribed circle: U[6.5; -0]
Coordinates of the inscribed circle: I[10; 2]

Exterior (or external, outer) angles of the triangle:
∠ A' = α' = 112.6219864948° = 112°37'11″ = 1.17660052071 rad
∠ B' = β' = 157.3880135052° = 157°22'49″ = 0.39547911197 rad
∠ C' = γ' = 90° = 1.57107963268 rad

# How did we calculate this triangle?

The calculation of the triangle progress in two phases. The first phase is such that we try to calculate all three sides of the triangle from the input parameters. The first phase is different for the different triangles query entered. The second phase is the calculation of other characteristics of the triangle, such as angles, area, perimeter, heights, the center of gravity, circle radii, etc. Some input data also results in two to three correct triangle solutions (e.g., if the specified triangle area and two sides - typically resulting in both acute and obtuse) triangle).

### 1. Input data entered: cathetus a and cathetus b

$a = 12 \ \\ b = 5$

### 2. From cathetus a and cathetus b we calculate hypotenuse c - Pythagorean theorem:

$c^2 = a^2+b^2 \ \\ c = \sqrt{ a^2+b^2 } = \sqrt{ 12^2 + 5^2 } = \sqrt{ 169 } = 13$

Now we know the lengths of all three sides of the triangle, and the triangle is uniquely determined. Next, we calculate another its characteristics - same procedure as calculation of the triangle from the known three sides SSS.

$a = 12 \ \\ b = 5 \ \\ c = 13$

### 3. The triangle perimeter is the sum of the lengths of its three sides

$p = a+b+c = 12+5+13 = 30$

### 4. Semiperimeter of the triangle

The semiperimeter of the triangle is half its perimeter. The semiperimeter frequently appears in formulas for triangles that it is given a separate name. By the triangle inequality, the longest side length of a triangle is less than the semiperimeter.

$s = \dfrac{ p }{ 2 } = \dfrac{ 30 }{ 2 } = 15$

### 5. The triangle area - from two legs

$T = \dfrac{ ab }{ 2 } = \dfrac{ 12 \cdot \ 5 }{ 2 } = 30$

### 6. Calculate the heights of the right triangle from its area.

$h _a = b = 5 \ \\ \ \\ h _b = a = 12 \ \\ \ \\ T = \dfrac{ c h _c }{ 2 } \ \\ \ \\ \ \\ h _c = \dfrac{ 2 \ T }{ c } = \dfrac{ 2 \cdot \ 30 }{ 13 } = 4.62$

### 7. Calculation of the inner angles of the triangle - basic use of sine function

$\sin α = \dfrac{ a }{ c } \ \\ α = \arcsin(\dfrac{ a }{ c } ) = \arcsin(\dfrac{ 12 }{ 13 } ) = 67^\circ 22'49" \ \\ \sin β = \dfrac{ b }{ c } \ \\ β = \arcsin(\dfrac{ b }{ c } ) = \arcsin(\dfrac{ 5 }{ 13 } ) = 22^\circ 37'11" \ \\ γ = 90^\circ$

An incircle of a triangle is a circle which is tangent to each side. An incircle center is called incenter and has a radius named inradius. All triangles have an incenter, and it always lies inside the triangle. The incenter is the intersection of the three angle bisectors. The product of the inradius and semiperimeter (half the perimeter) of a triangle is its area.

$T = rs \ \\ r = \dfrac{ T }{ s } = \dfrac{ 30 }{ 15 } = 2$

The circumcircle of a triangle is a circle that passes through all of the triangle's vertices, and the circumradius of a triangle is the radius of the triangle's circumcircle. Circumcenter (center of circumcircle) is the point where the perpendicular bisectors of a triangle intersect.

$R = \dfrac{ c }{ 2 } = \dfrac{ 13 }{ 2 } = 6.5$

### 10. Calculation of medians

A median of a triangle is a line segment joining a vertex to the midpoint of the opposite side. Every triangle has three medians, and they all intersect each other at the triangle's centroid. The centroid divides each median into parts in the ratio 2:1, with the centroid being twice as close to the midpoint of a side as it is to the opposite vertex. We use Apollonius's theorem to calculate the length of a median from the lengths of its side.

$m_a^2 = b^2 + (a/2)^2 \ \\ m_a = \sqrt{ b^2 + (a/2)^2 } = \sqrt{ 5^2 + (12/2)^2 } = 7.81 \ \\ \ \\ m_b^2 = a^2 + (b/2)^2 \ \\ m_b = \sqrt{ a^2 + (b/2)^2 } = \sqrt{ 12^2 + (5/2)^2 } = 12.258 \ \\ \ \\ m_c = R = \dfrac{ c }{ 2 } = \dfrac{ 13 }{ 2 } = 6.5$

The right triangle calculators compute angles, sides (adjacent, opposite, hypotenuse) and area of any right-angled triangle and use it in the real world. Two independent properties entirely determine any right-angled triangle. The calculator provides a step-by-step explanation for each calculation.

A right triangle is a kind of triangle that has one angle that measures C=90°. In a Right triangle, the side c that is opposite of the C=90° angle, is the longest side of the triangle and is called the hypotenuse. The variables a, b are the lengths of the shorter sides, also called legs or arms. Variables for angles are A, B, or α (alpha) and β (beta). Variable h refers to the altitude(height) of the triangle, which is the length from the vertex C to the hypotenuse of the triangle.

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