Verified answer

1) 9x²+12x+4-12x-40=0

9x²-36=0

x²-4=0

(x-2)(x+2)=0

x1= -2,   x2= 2

2) x²-1=2(x²-4)

x²-1-2x²+8=0

-x²+7=0

x²-7=0

(x-√7)(x+√7)=0

x1= -√7,         x2= √7

3) 48-3(x²-5)²=0

16-(x²-5)²=0

(4-(x²-5))*(4+(x²-5))=0

(4-x²+5)(4+x²-5)=0

(9-x²)(x²-1)=0

(3-x)(3+x)(x-1)(x+1)=0

x1=3,     x2= -3,     x3=1,    x4= -1