http://www.webmaths.co.uk/Powerpoint%20presentations/Shape,%20Space%20and%20Measure/Loci.ppt
https://www.slideshare.net/estelav/locus-1
http://www.whiteboardmaths.com/product_63.html
https://slideplayer.com/slide/4497663/
https://www.interactive-maths.com/uploads/1/1/3/4/11345755/smarties_loci.ppt
KLB BOOK 4 MATHEMATICS