Question

(7a-6b+5c)²..........................: ​

Answer 1

Answer:

49a^2+36b^2+25c^2-84ab-70ac ans

Step-by-step explanation:

let a = 7a, b = 6b and c= 5c

so (a+b+c)^2 = a^2+b^2+c^2-2ab-2bc+2ac

so and = (7a) ^2+(6b)^2+(5c) ^2-2*7a*6b-2*6b*5c+2*5c*7a

= 49a^2+36b^2+25c^2-84ab-70ac ans

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Answer 2

Step-by-step explanation:

formula = a² +b² +c²+ 2ab+ 2bc+ 2ac

(7a – 6b + 5c)2 +(7a + 6b – 5c)2 = [(7a)2 +(- 6b)2 +(5c)2 +{2 ×(7a)×(- 6b)} +{2 ×(- 6b)× (5c)} +{2 ×(7a)×(5c)} ] + [(7a)2 +(6b)2 +(- 5c)2 +{2 ×(7a)×(6b)} +{2 ×(6b)× (- 5c)} +{2 ×(7a)×(-5c)} ]

{ ∵(a + b + c)2 = a2 + b2 + c2 + 2ab + 2bc + 2ac }

= [ 49a2 + 36b2 + 25c2+{ – 84ab } +{– 60bc } + { 70ac } ] + [ 49a2 + 36b2 + 25c2 +{84ab } + { - 60bc} +{– 70ac } ]

= [ 49a2 + 36b2 + 25c2 – 84ab – 60bc + 70ac ] + [ 49a2 + 36b2 + 25c2 + 84ab – 60bc – 70ac ]

= 49a2 + 36b2 + 25c2 – 84ab – 60bc + 70ac + 49a2 + 36b2 + 25c2 + 84ab – 60bc – 70ac

= 98a2 + 72b2 + 50c2 – 120bc