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A binary operation * on the set (0, 1, 2, 3, 4, 5) is defined as \(a*b=\begin{cases}a+b;\quad if&a+b<6\\a+b-6;\quad if&a+b\geq6\end{cases}\)Show that 0 is the identity for this operation and each element a has an inverse (6 - a) |
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Answer» To find: identity and inverse element For a binary operation if a*e = a, then e s called the right identity If e*a = a then e is called the left identity For the given binary operation, e*b = b ⇒ e + b = b ⇒ e = 0 which is less than 6. b*e = b ⇒ b + e = b ⇒ e = 0 which is less than 6 For the 2nd condition, e*b = b ⇒ e + b - 6 = b ⇒ e = 6 But e = 6 does not belong to the given set (0,1,2,3,4,5) So the identity element is 0 An element c is said to be the inverse of a, if a*c = e where e is the identity element (in our case it is 0) a*c = e ⇒ a + c = e ⇒ a + c = 0 ⇒ c = - a a belongs to (0,1,2,3,4,5) - a belongs to (0, - 1, - 2, - 3, - 4, - 5) So c belongs to (0, - 1, - 2, - 3, - 4, - 5) So c = - a is not the inverse for all elements a Putting in the 2nd condition a*c = e ⇒ a + c - 6 = 0 ⇒ c = 6 - a 0≤a<6 ⇒ - 6≤ - a<0⇒ 0≤6 - a<60≤c<5 So c belongs to the given set Hence the inverse of the element a is (6 - a) Hence proved |
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