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A4. Real numbers : surds. Numbers such as 2 or 3 are called surds. In fact any number which can be written using a square root symbol is called a surd. These are all surds: 77, 3+2, 101-61, 5/3... Some surds can be simplified a little: 12=(3 x 4)=3 x 2=23 96=(6 x 16)=6 x 16=46 Some numbers can be simplified further so that they no longer have a square root. In this case they are not called surds: 4=2 225=2 x 5=10 You can do arithmetic with surds: 77 x 77=77, 3 + 3=23, 57 - 27=37