दर्शाइए कि :
(i) `(3x+7)^2-84x=(3x-7)^2`
(ii) ` (9p-5q)^2+180pq=(9p+5q)^2`
(iii) ` ((4)/(3)m-(3)/(4)n)^2+2"mm"=(16)/(9) m^2+(9)/(16)n^2`
(iv) `(4pq+3q)^2-(4pq-3q)^2=48pq^2`
(iv) ` (a-b)(a+b)+(b-c)(b+c)+(c-a)(c+a)=0`