4x² +24x-64

First of all, it is seen that 4 is a common factor to all the terms, hence we take it out

=4( x² +6x-16)

Now x²+6x-64 can be factorised by splitting the middle term 6x as 8x-2x, as shown below:

=4(x² +8x-2x -16)

=4[ (x² +8x) – (2x+16)]

=4[ x(x+8) -2(x+8)}

=4 (x+8)(x-2)

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