The third triangle number is 6.
90
The supplementary angle of the triangle.
Any number between 3 and 15
Any number between 8-16 If you do 12+5=17 the other side can't be 17 because then the triangle would be flat so it's any number lower than 17. Also, 12-5= 7. Again, 7 can't be the third side of this traingle because it would make the triangle flat. so any number higher than 7 would work.
Assuming you mean the third angle of a triangle... 64 degrees.
90
Any three numbers where the sum of the two smaller numbers is greater than the third number. List the numbers in order from least to greatest, repeating any number if necessary. Add the first two numbers together and if this sum is greater than the third number then a triangle with those sides can be made. ie if the sum of the two smaller numbers is greater than the third number then a triangle can be made.
The supplementary angle of the triangle.
18
Any number between 3 and 15
If I remember correctly, the triangle numbers are 1, 3, 6, 10, 15... It is like racking up billiard balls or bowling pins. If the first number is 1, then the 3rd number is 6.
The third angle of a triangle is equal to 180 degrees minus (the sum of the first two angles).
An isosceles triangle.
Any number between 8-16 If you do 12+5=17 the other side can't be 17 because then the triangle would be flat so it's any number lower than 17. Also, 12-5= 7. Again, 7 can't be the third side of this traingle because it would make the triangle flat. so any number higher than 7 would work.
...a right triangle.
If two angles of one triangle are congruent to two angles of another triangle, then the third angles are also congruent.
Two angles of a triangle add up to 65°. What is the measure of the third angle?