Posted by **Cindy** on Wednesday, December 14, 2011 at 9:25pm.

A triangle has side lengths of 18 cm, 80 cm, and 81 cm. Classify it as acute, obtuse, or right

- geometry -
**drwls**, Thursday, December 15, 2011 at 6:28am
With two long, almost equal, sides and a short side, you can visualize it in your head. It is acute.

It certainly is not a right angle, since 18^2 + 80^2 does not equal 81^2.

The law of cosines can be used to answer the problem numerically.

The largest angle C is opposite the longest side, c.

c^2 = a^2 + b^2 -2ab cosC

When c^2 < (a^2 + b^2), as it is here, cosC must be positive, making C an acute angle.

## Answer This Question

## Related Questions

- geometry - classify a triangle with side lengths 5, 9 and 12 as acute, right, or...
- Geometry - A triangle has side lengths of 18 cm, 80 cm, and 81 cm. Classify it ...
- Geometry - Tell if the measures 9,11, and 7 can be side lengths of a triangle. ...
- geometry - A triangle has side lengths of 14 cm, 48 cm, and 50 cm is it acute, ...
- Geometry Part 2 - A triangle has side lengths 10,15,and 7.Is the triangle acute,...
- Math - Again i wrote the question wrong. 4. Classify the triangle with angles ...
- Geometry - 1. The sides of a triangle have lenghts x, x+4, and 20. Specify those...
- Math - A triangle has side lengths 10, 15, and 7. Is the triangle acute, obtuse...
- geometry - Suppose a triangle has side lengths of 6, 7, and 10. What best ...
- Help me - 11. Name the triangles that are classified by angles. right, scalene, ...

More Related Questions