we can't solve first 2 because of missing diagramd
but, longest side=hypotonuse=c
other 2 sides=legs=a and b
a^2+b^2=c^2

last 2
1.
remember that
longest side<sum of other 2 sides or else you can't make a traignel
5+7=12
12<13
13 is longest side
13<12 is false
therefor it is false that it is a triangle
not a triangle
2.

so

=

rationalize denomeator by multplying by

