Let f:R→R be the function f(x)=(x−a1)(x−a2)+(x−a2)(x−a3)+(x−a3)(x−a1) with a1,a2,a3∈R. Then f(x)≥0 if and only if
A
At least two of a1,a2,a3 are equal
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B
a1=a2=a3
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C
a1,a2,a3 are all distinct
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D
a1,a2,a3 are all positive and distinct
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Solution
The correct option is Aa1=a2=a3 f(x)=(x−x1)+(x−x2)+(x−x3)f(x)=x2−2(a1+a2+a2)x+a1a2+a2a2+a2a2f(x)≥0D≤04(a1+a2+a2)2−4×1×(a1a2+a2a2+a2a2)≤0a21+a22+a23−a1a2−a2a2−a2a2≤012[(a1−a2)2+(a2−a3)2+(a3−a1)2]≤0
All the terms are perfect square so they cant be less than 0