[tex] 2(l^{2}+16l -57)=0 \\2(l^{2}+16l -57)=0 \\2(l^{2}+16l+3l-3l -57)=0 \\2[(l^{2}+19l)-(3l+57))]=0 \\2[l(l +19 )-3(3 +19))]=0 \\2(l+19)(l-3)=0 \\ l+19=0 \ \ \ or \ \ \l-3=0 \\l=-19 \ \ l<0 \\or\\ l=3 \\ \\ Answer : \ The \ length \ of \ a \ side \ is 3 \ cm.[/tex]
