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a+b+c =0
=>a^2+b^2+c^2 +2ac+2ab+2bc = 0
mà a^2 + b^2+c^2 = 1
=> 2ac+2ab+2bc = -1
=> ac+ab+bc = -1/2
=>a^2c^2+a^2b^2+b^2c^2 + 2ac+2ab+2bc = 1/4
=>a^2c^2+a^2b^2 + b^2c^2 -1 = 1/4
=> a^2c^2+a^2b^2+b^2c^2 = 5/4
Típ
a^2+b^2+c^2 = 1
=> a^4+b^4+c^4 + 2a^2b^2+2a^2c^2+2b^2c^2 = 1
=>a^4+b^4+c^4 + 2(a^2b^2+a^2c^2+b^2c^2) = 1
=> a^4+b^4+c^4 + 2*(5/4)=1
=> a^4+b^4+c^4 = -3/2