\(1)x^2-9=0\)
\(x^2-3^2=0\)
\(\left(x-3\right).\left(x+3\right)=0\)
\(TH1:x-3=0\)
\(x=3\)
\(TH2:x+3=0\)
\(x=-3\)
\(Vậyx\in\left\lbrace\underline{+}3\right\rbrace\)
\(2)25-x^2=0\)
\(5^2-x^2=0\)
\(\left(5-x\right).\left(5+x\right)=0\)
\(TH1:5-x=0\)
\(x=5\)
\(TH2:5+x=0\)
\(x=-5\)
\(Vậyx\in\left\lbrace-5;5\right\rbrace\)
\(3)-x^2+36=0\)
\(-\left(x^2-36\right)=0\)
\(-\left(x^2-6^2\right)=0\)
\(-\left(x-6\right).\left(x+6\right)=0\)
\(TH1:-\left(x-6\right)=0\)
\(-x+6=0\)
\(-x=-6\)
\(x=6\)
\(TH2:x+6=0\)
\(x=-6\)
\(Vậyx\in\left\lbrace-6;6\right\rbrace\)

1) 4x^4 - 4x^2 + 1
= (2x^2)^2 - 2.2x^2.1 + 1^2
= (2x^2 - 1)^2
2) 4x^2 - 12x + 9
= (2x)^2 - 2.2x.3 + 3^2
= (2x - 3)^2
3) 36 + x^2 -12x
= x^2 -12x + 36
= x^2 - 2.x.6 + 6^2
= (x - 6)^2

Key đây nhen!!!
1 đến 10 ok r nha
11. C
12. A
13. A
14. B
15. A
16. A
17. B
18. D
19. A
20. C
21. C
22. A
23. B
24. B
25. B
26. C
27. D
28. B
29. A
30. B
31. A
32. C
33. D
34. C
35. A
36. D
37. A
38. D
39. C
40. A

Ghi vb ra dc k ạ? Có j mik giúp ạ.

2448 : [199 - (x - 6)] = 24
199 - (x - 6) = 2448 : 24
199 - x + 6 = 102
205 - x = 102
x = 205 - 102
x = 103
Vậy x = 103.