l2

• U - universal
• E - is an element
• ∉ - is not an element of
• {} / ∅ - empty set or null set
• set builder notation - infinite set
• finite - if the number of a set is a whole number
• natural num or counting numbers N = {1, 2, 3, 4, 5, ...}
• whole numbers W - {0, 1, 2 ,3 ,4 ,5, ...}
• integer I = {.... -4, -3, -2, -1 , 0, 1, 2, 3, 4, ...}
• rational number Q={0.5,0.333...,0.75,0.8333...,…}

• irrational numbers Ȋ ={√2​, √3​, √5​,π,e,ϕ, √7​, √11​, √13​,…}

• real numbers R={−3,−21​,0,1, √2​,π,2.5, √3​, 7/4​,…}