1.

Expand : (x + 2y + 3z)2

Answer»

We know that, 

(a + b + c)2 = a2 + b2 + c2 + 2ab + 2bc + 2ca 

Substituting, a = x, b = 2y and c = 3z 

(x + 2y + 3z)2 = x2 + (2y)2 + (3z)2 + 2(x)(2y) + 2(2y)(3z) + 2(3z)(x) 

= x2 + 4y2 + 9z2 + 4xy + 12y2 + 6zx



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