book Maths Puzzle Numerical Ability

ok well i'm totally confused about radicals

(the radican sign and 2 inside of it + 7) then the same thing but minus 4

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book Other Question

Express irrational solutions in simplest radical form.

N^2-6=0 Would this be (+-)Sqrt 5?

(n-5)^2=20 Would this be (+-)2*Sqrt 5? what is the gradient of a line on a graph that is parallel to y=3x?