State with reasons, which of the following pairs of terms are of like terms and which are of unlike terms : (i) `7x, 12y` (ii) `15x-21x` (iii) `4ab,7ba`

Explanation

(i) `7x = 7 xx x`

`12y = 2 xx 2 xx 3 xx y` so, unlike

(ii) `-21x = -3 xx 7 xx x`

`15x = 3 xx 5 xx x` so, like

(iii) `-4ab = -2 xx 2 xx a xx b`

`7ba = 7 xx b xx a ` like

(iv) `3xy = 3 xx x xx y `

`3x = 3 xx x` unlike

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