How do you find the area of a triangle if you only know it's three sides?

You would have to find the height.

To do this, you cut the triangle from the upper vertex to the base to create two new triangles.

Then you use the Law of Cosines. You could use the google calculator for this by searching “law of cosines calculator” and inputting the values, but in case of a test, the formula is a^2 = b^2 + c^2 - 2bc cosA

If you could provide an example of a triangle, I will gladly help you with the steps! Hope this helped!