$$(4a+3b+2c)^{2}$$
= $$(4a)^2 + (3b)^2 +Â (2c)^2 + 2(4a.3b +Â 3b.2c +Â 2c.4a)$$
($$\because (a + b + c)^2 = a^2 + b^2 + c^2 + 2(a + b + c))$$
= $$16a^2 +Â 9b^2 + 4c^2 + 2(12ab + 6bc + 8ac)$$
= $$16a^2 + 9b^2 + 4c^2 + 24ab + 12bc + 16ac$$
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