Isosceles Triangle Calculator
Solve an isosceles triangle from any two of its leg, base, base angle, vertex angle, height, area and perimeter.
Change the values and press Calculate to work out your own figures.
Enter any two values, including at least one length.
Show the working
- From the leg a and base b
- h = √(a² − (b/2)²); cos α = (b/2) ÷ a; β = 180° − 2α
How to use it
Enter any two values, including at least one length.
Enter the values you know (decimals, fractions, surds such as 2√5, or angles such as π/3 in radians). Show the working gives the rule used at each step.
Key facts
h = √(a² − (b/2)²); β = 180° − 2α
Two equal angles
The base angles are equal and the height from the vertex bisects the base.
Questions
What is the area with legs 3 and base 5?
≈ 4.145780988.
Can the base be longer than twice the leg?
No: then the legs can't meet.
Formulas
h = √(a² − (b/2)²); β = 180° − 2α
Sources
Limitations
- Angles can be typed in degrees or radians; radians may be written with π (π/3, 2pi/3).