There are different formulae, depending on what you DO know. Here you will find several: http://en.wikipedia.org/wiki/Triangle#Computing_the_area_of_a_triangle
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You find the height by using Pythagoras' theorem and then 0.5*base*height = area.
Without knowing its base its almost impossible to give a correct answer.
-- Imagine what you have if you slice the triangle in half along the height ...-- You have a right triangle. One side of it is 1/2 of the base, and one side isthe height.-- The slanting side is the hypotenuse of the right triangle, and knowing whatyou know about right triangles, you can calculate its length.-- Once you do that, you have the lengths of all three sides of the original triangle,and you can calculate the perimeter.
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The area of a triangle is base x height / 2. Height should be perpendicular to base.