if a triangle has 3 side one is 12 one is 72 what is the last sude

this triangle has 3 sides one is 12, lets call this side a²another side is 72, lets call this side c²this triangle must follow Pythagoras therom if it is right angled, that is a²+b²=c²where a and b are the two shorter sides and c is the longest side (called the hypotenuse) opposite the right angleto find the last side you do 72² - 12² = 5040but it is the square root of 5040 which is 70.99 (two decimal places) if you want it in decimal form, if you want it in surd form it is √5040

There is no way to answer that with only the information given.  The 3rd side can be ANY length between 60 and 84.  You can't solve a triangle if you only know 2 sides of it.