Sydney - the others are capital cities
Yeats - the others are Poets laureate
bit confused about the 3rd one ... scalene, isosceles & equilateral are all sorts of triangles, hypotenuse is a side on a right angled triangle, and a trapezium is a 4-sided figure.... so either hypotenuse (not a shape but a line) or trapezium (not a word associated with triangles)