Question

1.x(x-3)=4 means that x=4 and x-3=4
Is that right?


2.Is the sum of squares prime???

Answer 1

1. no it doesn't
even though by coincidence x = 4 does work, your other solution of x = 7 does not.
What you are assuming to be true only works if the Right Side is equal to zero.
in this case you have to expand it, ..
x^2 - 3x - 4 = 0
(x-4)(x+1) = 0
then x = 4 and x = -1

2. true, because it has no factors other than 1 and itself

Answer 2

.x(x-3)=4 means that x=4 and x-3=4
Is that right?

x^2-3x-4=0

(x-4)(x+1)=0

x1=4 and x2=-1

so if you put x = 4 then x-3 can't be equell to 4

Answer 3

the rule is this: A prime can be written as a sum of
two squares. I hope that helps