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Show that. (i) `(3x+7)2-84x=(3x-7)2` (ii) `(9p-5q)2+180pq=(9p+5q)2` (iii) `(43(m)-34(n))2+2mn=169(m2)+916(n2)` (iv) `(4pq+3q)2-(4pq-3q)2=48pq2` (v) `(a-b)(a+b)+(b-c)(b+c)+(c-a)(c+a)=0` |
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Answer» (i) `L.H.S. = (3x+7)^2 -84x = 9x^2+49+42x - 84x = 9x^2+49-42x` ` = (3x)^2+(7)^2 - 2**3x**7 = (3x-7)^2 = R.H.S.` (ii)`L.H.S. = (9p-5q)^2+180pq = (9p)^2+(5q)^2-90pq+180pq` `=(9p)^2+(5q)^2+90pq = (9p)^2+(5q)^2+2(9p)(5q) ` `= (9p+5q)^2 = R.H.S.` (iii)`L.H.S. = (4/3m-3/4n)^2 +2mn= (4/3m)^2+(3/4n)^2 - 2**(4/3m)**(3/4n)+2mn` `=16/9m^2+9/16n^2+2mn-2mn = 16/9m^2+9/16n^2 = R.H.S.` (iv)`L.H.S. = (4pq+3q)^2-(4pq-3q)^2` Here, we will use `(a+b)(a-b) = a^2-b^2` So, `L.H.S. = (4pq+3q+4pq-3q)(4pq+3q-4pq+3q)` ` = 8pq**6q = 48pq^2 = R.H.S.` (v)`L.H.S. = (a-b)(a+b)+(b-c)(b+c)+(c-a)(c+a)` `= a^2-b^2+b^2-c^2+c^2-a^2 = 0 = R.H.S.` |
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