Question 165098
Let x be 2 of the sides & y be the third side.
2x+y=80
y=80-2x
xy=700
x(80-2x)=700
80x-2x^2-700=0
2x^2-80x+700=0
2(x^2-40x+350)=0
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 
x=(40+-sqrt[-40^2-4*1*350])/2*1
x=(-40+-sqrt[1600-1400])/2
x=(40+-sqrt200)/2
x=(40+-14.142)/2
x=(40+14.142)/2
x=54.142/2
x=27.07 
y=80-2*27.07
y=80-54.14
y=25.86
x=(40-14.142)/2
x=25.858/2
x=12.929
y=80-2*12.929
y=80-25.858
y=54.142