设a.b.c∈R+且a+b=c,求证a^2/3+b^2/3>c2/3

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设a.b.c∈R+且a+b=c,求证a^2/3+b^2/3>c2/3

设a.b.c∈R+且a+b=c,求证a^2/3+b^2/3>c2/3
设a.b.c∈R+且a+b=c,求证a^2/3+b^2/3>c2/3

设a.b.c∈R+且a+b=c,求证a^2/3+b^2/3>c2/3
证明:欲证a^2/3+b^2/3>c^2/3
即证a^2+3a^(4/3)b^(2/3)+3a^(2/3)b^(4/3)+b^2>c^2
只需证(a+b)^2-2ab+3a^(4/3)b^(2/3)
+3a^(2/3)b^(4/3)+b^2>c^2
∵a+b=c,∴(a+b)^2=c^2
只需证
3a^(2/3)b^(2/3)[a^(2/3)+b^(2/3)]>2ab
只需证a^(2/3)+b^(2/3)>2/3*a^(1/3)b^(1/3)
∵a^(2/3)+b^(2/3)≥2a^(1/3)b^(1/3),
∴a^(2/3)+b^(2/3)>2/3*a^(1/3)b^(1/3)成立,原不等式得证.

a+b=c
a=c-b
a^2=(c-b)^2
要证明 a^2/3+b^2/3>c2/3 对两边同时3次方
(a^2/3+b^2/3)^3>c2证明(a^2/3+b^2/3)^3>c2就可以了
(a^2/3+b^2/3)^3=a^2+3a^4/3b+3(a^2/3+b^2/3)^2+b^2=a^2+b^2+2ab+3a^4/3b+3(a^2/3+b^2/...

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a+b=c
a=c-b
a^2=(c-b)^2
要证明 a^2/3+b^2/3>c2/3 对两边同时3次方
(a^2/3+b^2/3)^3>c2证明(a^2/3+b^2/3)^3>c2就可以了
(a^2/3+b^2/3)^3=a^2+3a^4/3b+3(a^2/3+b^2/3)^2+b^2=a^2+b^2+2ab+3a^4/3b+3(a^2/3+b^2/3)^2-2ab=c^2+3a^4/3b+3(a^2/3+b^2/3)^2-2ab
3a^4/3b+3(a^2/3+b^2/3)^2-2ab>0所以(a^2/3+b^2/3)^3>c2即 a^2/3+b^2/3>c2/3

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