N4
(7-x)^2-x^2=21
49-14x+x^2-x^2= 21
-14x=21-49
-14x = -28
x=2
(x+5)(x-5)-(x-4)^2>15
x^2-25-(x^2-8x-16)>15
x^2-25-x^2+8x-16>15
-41+8x>15
8x>15+41
8x>56
x>7
49-14x+x^2-x^2=21
49-14x=21
-14x=-28
