What if I only know one leg and that one of the angles is equal to 45degrees?

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If you're looking at a right triangle, and one of the non-90 degree angles is 45, then the third angle is 45 as well.  45-45-90 triangles are special in that the ratio of the sides is 1-1-sqrt(2). In other words, the hypotenuse will always be sqrt(2) times the length of the legs.So if you know one leg as x, then the other leg is x also, and the hypotenuse is x*sqrt(2)