1.

Factorize `x^2-4x-21`.

Answer» The given expression is `x^2-4x-21`.
We split -4 into two whose sum is -4 and product -21.
` therefore x^2-4x-21 =x^2-7x+3x-21`.
`=x(x-7)+3(x-7)`
`=(x-7)(x+3)`.
Hence, `x^2-4x-21=(x-7)(x+3)`.


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