Question

plzz plzzz answer this question

Answer 1

LHS:
(5x-7)^2 + 140x
25x^2 - 2*5x*7 + 49 + 140x......[identity:(a-b)^2]
25x^2 -70x + 49 + 140x = 25x^2 + 70x + 49
L.H.S = 25x^2 + 70x + 49....(i)

R.H.S
(5x+7)^2 = 25x^2 + 2*5x*7 + 49 = 25x^2 + 70x + 49
R.H.S = 25x^2 + 70x + 49.....(ii)
Compare (i) and (ii)...L.H.S = R.H.S
Hence (5x-7)^2 + 140x = (5x+7)^2...hence proved
Hope it helps.

Answer 2

(5x-7)^2 + 140x =  {(5x)^2 -2(5x)(7) + 7^2} +140x     [(a-b)^2 = a^2 - 2ab + b^2]
                          = 25x^2 - 70x + 49 +140x
                          = 25x^2 + 70x + 49
                          = (5x)^2 + 2(5x)(7) + (7)^2
                          = (5x+7)^2                                       [a^2 + 2ab + b^2 = (a+b)^2]
HENCE PROVED.
Hope it helps you...