## Answer :

c represents the longest side of the triangle

If the triangle is a right triangle, the Pythagorean theorem will be true.

(1) 10,24,26

[tex]10^2 + 24^2 = 676[/tex]

[tex]26^2 = 676[/tex]

[tex]10^2 + 24^2 = 26^2[/tex]

Right Triangle

(2) 12,18,20

[tex]12^2 + 18^2 = 468[/tex]

[tex]20^2 = 400[/tex]

[tex]12^2 + 18^2 \neq 20^2[/tex]

Not a right triangle

(3) 15,26,30

[tex]15^2 + 26^2 = 901[/tex]

[tex]30^2 = 900[/tex]

[tex]15^2 + 26^2 \neq 30^2[/tex]

Not a right triangle

(4) 40,50,80

[tex]40^2 + 50^2 = 4100[/tex]

[tex]80^2 = 6400[/tex]

[tex]40^2+50^2 \neq 80^2[/tex]

Not a right triangle

#1 is a right triangle