Bonjour ;
1)
[tex](x^2 - 13)^2 - 144 = x^4 -26x^2 + 169 -144 = x^4 - 26x^2 + 25 .[/tex]
2)
[tex]x^4 - 26x^2 + 25= (x^2 - 13)^2 - 144 = (x^2 - 13)^2 - 12^2\\\\ = (x^2 - 13 - 12)(x^2 - 13 + 12) = (x^2 -25)(x^2 - 1)\\\\ = (x^2 -5^2)(x^2 - 1) = (x - 5)(x + 5)(x - 1)(x + 1) = 0\\\\ \textit{ donc : } x = 5 ; x = - 5 ; x = 1 ; x = - 1 .[/tex]