What Type of Angle?

Acute TriangleAll angles are less than 90° 

Right TriangleHas a right angle (90°) 

Obtuse TriangleHas an angle more than 90° 
Right Isosceles TriangleHas a right angle (90°), and also two equal angles 
The area is half of the base times height.


Area = ½bh 
The formula works for all triangles.
Another way of writing the formula is bh/2
Height = h = 12
Base = b = 20
Area = bh/2 = 20 × 12 / 2 = 120
Just make sure that the "h" is measured at right angles to the "b".
Why is the Area "Half of bh"?Imagine you "doubled" the triangle (flip it around one of the upper edges) to make a squarelike shape (it would be a "parallelogram" actually), THEN the whole area would be bh (that would be for both triangles, so just one is ½bh), like this: 
You can also see that if you sliced the new triangle and placed the sliced part on the other side you get a simple rectangle, whose area is bh. 