If the square and equilateral triangle have the same side length, a square would have a larger area.
Use these are equations and you can see which one is greater.
Square area with side length s: s^2
Equilateral triangle area: s^2 * (√3 ) / 4
(√3) / 4 < 1, if you didn't know
I hope this helps. Have an awesome day! :)