What is the value of $a^2 +4b^2 +9c^2 - 4ab +12bc - 6ca $ ?
Answer & explanation
Correct answer: option 4
We know that,
(a + b + c)² = a² + b² + c² + 2(ab + bc + ca)
a2 + 4b2 + 9c2 - 4ab + 12bc - 6ca
= a2 + 4b2 + 9c2 - 4ab + 12bc - 6ca
= (a)² + (-2b)² +(-3c)² +2[ a(-2b) + (-2b)(-3c) + a(-3c) ]
a2 + 4b2 + 9c2 - 4ab + 12bc - 6ca = (a - 2b - 3c)2