We study the necessary and sufficient conditions on the masses for the periodic solution of planar 4-body problems. where three particles locate at the vertices of an equilateral triangle and rotate with constant angular velocity about a resting particle. We prove that the above periodic motion is a solution of Newtonian 4-body problems if and only if the resting particle is at the or... https://cosmeticssquadets.shop/product-category/shower-cap/