Particle constrained by 4 springs SHM

[kate12]

A point mass is constrained to move in the horizontal plane. It is attached to four fixed pegs by four light springs. The four pegs are arranged at the corners of a square of side a√2. Each spring has natural length a/2 and spring constant k.

Show that the mass executes SHM with angular frequency ω=√(3k/m)


Now I keep getting that ω=√(2k/m). I don't understand where the 3k comes from.

 

[Liquidxlax]

show some work, and i can help