These two triangles are triangles that you often use in trigonometry.
A 30/60/90 triangle is a right scalene triangle with, as said angles of 30 degrees 60 degrees and 90 degrees. To find the dimensions of a 30/60/90 triangle you just have to remember that one side will equal x the other side will equal 2x and the third side will equal x multiplied by the radical (square root) of 3 (1.732...). A 45/45/90 triangle is an right isosceles triangle with angles of 2 45 degree angles and one 90 degree angle. The sides equal two sides being just x and one being x multiplied by the radical of 2 (1.414...). Please tell me if I did something wrong or if I should explain it better.