Elen, L.W.F..
Higher National Certificate Mathematics / - 1st ed / - London W8 : Cleaver-Hume Press Ltd. , 1963 - p.127 :
Mathematics
B / J9
Higher National Certificate Mathematics / - 1st ed / - London W8 : Cleaver-Hume Press Ltd. , 1963 - p.127 :
Mathematics
B / J9