Answer:
12
Step-by-step explanation:
Use Pythagorean theorem
[tex]a^2 +b^2 =c^2[/tex]
c= always hypotenuse/ longest side/ side across from right angle = 13
a= 5
[tex]5^2+b^2=13^2[/tex]
[tex]25+b^2=169[/tex]
Subtract 25 from 169
[tex]b^2= 144[/tex]
Square root both sides
b= 12
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it's also a special triangle known as a 5, 12, 13 triangle
