A polynomial (with integer coefficients) is solvable by radicals if its roots can each be expressed using standard arithmetic operations and square roots, cube roots, etc. Polynomial equations of degree up to 4 have long been known to be solvable by radicals. It was shown by Abel and later Galois that this is not generally the case for higher degrees; in fact, a polynomial is solvable by radicals if and only if its Galois group is a solvable group.