Since both 18 and -50 are even, we can start by factoring a 2 out of the expression:
[tex] 18-50z^2=2(9-25z^2) [/tex]
To factor [tex] 9-25z^2 [/tex], we can use the fact that, in general:
[tex] a^2-b^2=(a+b)(a-b) [/tex] for any two numbers a and b. Since 9 = 3² and 25z² = (5z)², we can rewrite and factor our expression using this fact:
[tex] 9-25z^2=3^2-(5z)^2=(3+5z)(3-5z) [/tex]
Altogether, our expression becomes
[tex] 2(3+5z)(3-5z) [/tex]
