User:Kernanjtcd/sandbox

I mhatamaitic, a deir aitheantais ceithre-cearnach Euler go bhfuil an táirge de dhá uimhir, gach ceann acu le suim cheithre cearnóga , é féin suim cheithre cearnóga. Go sonrach:
 * $$(a_1^2+a_2^2+a_3^2+a_4^2)(b_1^2+b_2^2+b_3^2+b_4^2)=\,$$


 * $$(a_1 b_1 - a_2 b_2 - a_3 b_3 - a_4 b_4)^2 +\,$$


 * $$(a_1 b_2 + a_2 b_1 + a_3 b_4 - a_4 b_3)^2 +\,$$


 * $$(a_1 b_3 - a_2 b_4 + a_3 b_1 + a_4 b_2)^2 +\,$$


 * $$(a_1 b_4 + a_2 b_3 - a_3 b_2 + a_4 b_1)^2.\,$$