$1 \,- 9\,x^2 = $   ?

$(1+3x)(1-3x)$ $(1+9x)(1-9x)$ $(1+3\,x^2)(1-3\,x^2)$ $(1-3x)^2$

$1 \,- 144\,x^2 = $   ?

$(1+144x)(1-144x)$ $(1-12x)^2$ $(1+12x)^2$ $(1+12x)(1-12x)$

$49 \,- 121\,y^2 = $   ?

$(49+11y)(49-11y)$ $(7+121y)(7-121y)$ $(7+11y)(7-11y)$ $(49+121y)(49-121y)$

$64\,y^2 \,- 144\,x^2 = $   ?

$(8y+12x)^2$ $(8y+144x)(8y-144x)$ $(8y+12x)(8y-12x)$ $(64y+12x)(64y-12x)$