How can you check to see if two ratios form a proportion?

Ratios can also be written as fractions. So when the ratios are in fraction form, they are proportionate if they are equivalent fractions.

for examplelets say if ur 2 ratios are 2:4 and 8:16put them in fraction form2/4 and 8/16
2/4 reduces to 1/2
8/16 reduces to 1/2
so these 2 ratios are proportionate because they are equivalent fractions

another exampleu have 2 ratios which are 3:5 and 6:12
3/5 and 6/12
3/5...does not reduce
6/12 = 1/2
these are not proportionate because they are not equivalent fractions

No a triangle cannot be formed because when you add the two smallest number together (which would be 11) the have to be bigger than the number it is "against" ( which would be 12)