The above graphic shows all 7 possible triangles that can exist.
CALCULATOR INSTRUCTIONS
Input 3 triangle side lengths (A, B and C), then click “ENTER”. This calculator will determine whether those 3 sides will form an equilateral, isoceles, acute, right or obtuse triangle or no triangle at all.
Without Using The Calculator
When given 3 triangle sides, to determine if the triangle is acute, right or obtuse:
1) Square all 3 sides.
2) Sum the squares of the 2 shortest sides.
3) Compare this sum to the square of the 3rd side.
if sum > (3rd side)2 Acute Triangle
if sum = (3rd side)2 Right Triangle
if sum < (3rd side)2 Obtuse Triangle
Here are three examples:
5, 6 and 7 Each side squared = 25, 36 and 49
sum of the squares of the short sides = 25 + 36 = 61
61 > 49 Acute Triangle
3, 4 and 5 Squaring each side = 9, 16 and 25
sum of the squares of the short sides = 9 + 16 = 25
25 = 25 Right Triangle
3, 7 and 9 Squaring each side = 9, 49 and 81
sum of the squares of the short sides = 9 + 49 = 58
58 < 81 Obtuse Triangle
For determining if the 3 sides can even form a triangle, the triangle inequality theorem states that the longest side must be shorter than the sum of the other 2 sides.