Question

Factor 405-5x^4

Answer 1

take 5 as a common factor

\[5(81 - x^4)\]

inside the brackets.. you have a difference of 2 squares if you consider

\[(x^2)^2\]

\[5(81 - (x^2)^2)\]

\[5(9 - x^2)(9+x^2)\]

last factorisation 9 - x^2 is the difference of 2 squares

solution

\[5(3-x)(3+x)(9+x^2)\]