*I'm not sure what you mean when to add and subtract but I hope this helps!
Answer:
Triangle1: 13
Triangle2: 25
Triangle3: 17
Explanation:
*Pythagorean Theorem Formula: a²+b²=c² where c is the hypotenuse (the side opposite of the right angle)
Triangle1:
1. Plug in the values into the Pythagorean Theorem Formula and simplify as shown below.
5²+12²=c²
25+144=c²
169=c²
c=√169
c=13
Triangle2:
1. Plug in the values into the Pythagorean Theorem Formula and simplify as shown below.
15²+20²=c²
225+400=c²
625=c²
c=√625
c=25
Triangle3:
1. Plug in the values into the Pythagorean Theorem Formula and simplify as shown below.
8²+15²=c²
64+225=c²
289=c²
c=√289
c=17