Question 903553
perimeter is 4s area is s^2
4s*4+1*s^2=561
16s+s^2=561
rearrange
s^2+16s-561=0
*[invoke change_this_name4450 1, 16, -561, "s"]

*[invoke complete_square "s", 1, 16, -561] 
discard negative answers
s=17