Factorise by proper substitution (x^2+4x)(x^2+4x-18)-63
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Answer:
(x-7)(x+3)(x+1)(x+3)
Step-by-step explanation:
(x^2+4x)(x^2+4x-18)-63
If we substitute x^2+4x=y, then
y(y-18)-63=y^2-18y-63=(y-21)(y+3)
Replacing y back with x^2+4x:
(x^2+4x)(x^2+4x-18)-63=
(x^2+4x-21)(x^2+4x+3)=
(x-7)(x+3)(x+1)(x+3)
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