How this calculator works
An oblique triangle may be acute or obtuse. The base-height rule works in both cases when the height is perpendicular to the base line. Three sides use Heron area; SAS uses the sine of the included angle; ASA first recovers the missing sides. Sided methods check that the triangle has no right angle. Base-height data alone cannot establish its angle class.
Formula
K = bh/2 = ab sin(C)/2; s = (a+b+c)/2; K = √[s(s-a)(s-b)(s-c)]; h_a = 2K/a; b = 2K/h.
Worked example
Sides 5 m, 5 m and 6 m have semiperimeter 8 m and area √(8×3×3×2) = 12 m². Heights to those sides are 4.8 m, 4.8 m and 4 m; each side-height product is 24 m².
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Frequently asked questions
Does oblique mean obtuse?
No. Oblique means the triangle has no right angle. All acute triangles and all obtuse triangles qualify.
Which measurement method should I use?
Use the set of measurements you actually have. Do not substitute a sloping side for a perpendicular height, and use the included angle for SAS.
Can I find a missing base?
Yes. Select the reverse base mode and supply a positive area and its matching perpendicular height. These two values do not determine the other sides.