if a+b+c=0 tgen find the value of a+³b³+c³
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a3+b3+c3=3abc
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As we know,
(a+b+c)³ = (a+b+c)² (a+b+c)
→(a+b+c)³ = a³ + b³ + c³ + a²(b+c) + b²(a+c) + c²(a+b) + 2(ab+bc+ac)(a+b+c)
= a³ + b³ + c³ + 3a²(b+c) + 3b²(a+c) + 3c²(a+b) + 6abc
So, (a+b+c)³ = a³ + b³ + c3 + 3(a+b)(b+c)(a+c)
From the last step:
→ a³ + b³ + c³ = (a+b+c)³ − [3a²(b+c) + 3b²(a+c) + 3c²(a+b) + 6abc]
So, a³ + b³ + c³ − 3abc
=(a+b+c)³ − [3a²(b+c) + 3b²(a+c) + 3c²(a+b) + 9abc]
Split 9abc among the three terms and now collect ab, bc & ac terms:
= (a+b+c)³ − [3ab(a+b+c) + 3bc(a+b+c) + 3ac(a+b+c)]
Take (a+b+c) as common outside,
=(a+b+c)[a²+b²+c²+2ab+2bc+2ac−3ab−3bc−3ac]
Thus we get:
a³ + b³ + c³ − 3abc=(a+b+c)[a² + b² + c² −ab−bc−ac]
which may further be rewritten as:
a³ + b³ + c³ − 3abc=(a+b+c)(1/2)[(a−b)²+(b−c)²+(a−c)²]
as (a−b)²=a²+b²−2ab
If a+b+c=0.
Clearly the RHS =0
So, a³ + b³ + c³ = 3abc
Thankyou!!!
(a+b+c)³ = (a+b+c)² (a+b+c)
→(a+b+c)³ = a³ + b³ + c³ + a²(b+c) + b²(a+c) + c²(a+b) + 2(ab+bc+ac)(a+b+c)
= a³ + b³ + c³ + 3a²(b+c) + 3b²(a+c) + 3c²(a+b) + 6abc
So, (a+b+c)³ = a³ + b³ + c3 + 3(a+b)(b+c)(a+c)
From the last step:
→ a³ + b³ + c³ = (a+b+c)³ − [3a²(b+c) + 3b²(a+c) + 3c²(a+b) + 6abc]
So, a³ + b³ + c³ − 3abc
=(a+b+c)³ − [3a²(b+c) + 3b²(a+c) + 3c²(a+b) + 9abc]
Split 9abc among the three terms and now collect ab, bc & ac terms:
= (a+b+c)³ − [3ab(a+b+c) + 3bc(a+b+c) + 3ac(a+b+c)]
Take (a+b+c) as common outside,
=(a+b+c)[a²+b²+c²+2ab+2bc+2ac−3ab−3bc−3ac]
Thus we get:
a³ + b³ + c³ − 3abc=(a+b+c)[a² + b² + c² −ab−bc−ac]
which may further be rewritten as:
a³ + b³ + c³ − 3abc=(a+b+c)(1/2)[(a−b)²+(b−c)²+(a−c)²]
as (a−b)²=a²+b²−2ab
If a+b+c=0.
Clearly the RHS =0
So, a³ + b³ + c³ = 3abc
Thankyou!!!
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