Algebra is a branch of mathematics in which we use variable for unknown quantity.
Ex: 1) ax = b or ax – b = 0
2) 3x – 9 = 3
when we solve these equation we get : 1) x = b/a and in 2) x = 4 . This means the value of x in both these equations are different and can have any value, it is not fixed.
You may have thought that from where this word ‘Algebra‘ came. This word came from the book Kitab al-muhtasar fi Hisab Aljaber w’al muqabalah written by Mohammed ibn Musa abu Abdullah al Khowarizmi of Baghdad around 825 A.D., but much before this , Aryabhatta and Brahmagupta had already done a lot of work in this field.