factorise \( 3 x^{4}-3 x^{2}-27 x^{2}+27 \)
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To factorise the expression \( 3x^{4} - 3x^{2} - 27x^{2} + 27 \), let's first combine like terms. The expression simplifies to: \( 3x^{4} - 30x^{2} + 27 \). Next, we can factor out a common factor of 3: \( 3(x^{4} - 10x^{2} + 9) \). Now, let’s set \( y = x^{2} \), which transforms the quadratic into: \( 3(y^{2} - 10y + 9) \). Now we can factor the quadratic: \( y^{2} - 10y + 9 = (y - 1)(y - 9) \). Substituting back for \( y \): \( 3((x^{2} - 1)(x^{2} - 9)) \). Recognising the difference of squares, \( x^{2} - 1 = (x - 1)(x + 1) \) and \( x^{2} - 9 = (x - 3)(x + 3) \): So, the final factorised form is: \( 3(x - 1)(x + 1)(x - 3)(x + 3) \).