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# Expand each of the following, using suitable identities: (iv) (3a - 7b - c)^2

4.(iv)   Expand each of the following, using suitable identities:

(iv)    $(3a - 7b - c)^2$

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Given is  $(3a - 7b - c)^2$

We will Use identity

$(x+y+z)^2=x^2+y^2+z^2+2xy+2yz+2zx$

Here, $x =3a , y = -7b \ \ and \ \ z = -c$

Therefore,

$(3a - 7b - c)^2=(3a)^2+(-7b)^2+(-c)^2+2.3a.(-7b)+2.(-7b).(-c)+2.(-c)$$.3a$

$= 9a^2+49b^2+c^2-42ab+14bc-6ca$

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