1.

Expand `(2a+3b+4c)^2`.

Answer» Putting `2a-x,3b=y and 4c=z`, we get
`(2a+3b+4c)^2`
`=(x+y+z)^2`
`=x^2+y^2+z^2+2xy+2yz+2zx`
` =(2a)^2+(3b)^2+(4c)^2+{2xx (2a) xx (3b)}+{2xx(3b)xx(4c)}+{2xx (4c)xx (2a)}`
`=4a62+9b^2+16c^2+12ab+24bc+2zx`.


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