/ ____________\ / ____________\ / ____________\ / ____________\ | / ____ | | / ____ | | / ____ | | / ____ | | / 9 \/ 21 | | / 9 \/ 21 | | / 9 \/ 21 | | / 9 \/ 21 | |x + / - - ------ |*|x - / - - ------ |*|x + / - + ------ |*|x - / - + ------ | \ \/ 2 2 / \ \/ 2 2 / \ \/ 2 2 / \ \/ 2 2 /
(((x + sqrt(9/2 - sqrt(21)/2))*(x - sqrt(9/2 - sqrt(21)/2)))*(x + sqrt(9/2 + sqrt(21)/2)))*(x - sqrt(9/2 + sqrt(21)/2))