Question : What is the value of the given expression?
$(a+b+c)^2-a^2-b^2-c^2$
Option 1: $2abc$
Option 2: $2(ab+bc+ca)$
Option 3: $2(a+b+c)$
Option 4: $2ab+bc-2ca$
Correct Answer: $2(ab+bc+ca)$
Solution :
By using the identity:
$(a+b+c)^{2} = a^{2}+b^{2}+c^{2}+2(ab+bc+ca)$
$\therefore$ $(a+b+c)^{2}- a^{2}- b^{2}- c^{2} = 2(ab+bc+ca)$.
Hence, the correct answer is $2(ab+bc+ca)$.
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