Isosceles triangle has two sides of equal length the third is 7 less than twice the length of one of the other sideside the perimeter is 44cm. what is the length i'd the 3rd side?

If your asking for the length of the third side, to find it first we have to build an equation.

let's take x as the length of the two sides with the same length. 
so your equation should be, 

x+x+2x-7=44cm 
=4x-7=44cm
     +7  +7
=4x=51cm
 ÷4   ÷4
=x=12.75cm

length of the sides with equal length= 12.75cm
length of the 3rd side= 12.75×2-7=18.5cm

check,
12.75cm+12.75cm+18.5cm=44cm
hope this helps