Verified answer

assuming your x2 is x^2,

5x^2-10z+20; you factor out the 5 which is common to all

5(x^2-2z+10)

x^2-64; is a special case of (a^2-b^2)=(a+b)(a-b)

(x^2-8^2)=(x+8)(x-8)

x^2-5x-14 ;

=(x-7)(x+2); you can check by expanding the two factors

6x^2+3x-30; factor out the 3

3(2x^2+x-15); then factor the quadratic

=3(2x-5)(x+3); can check by expanding