9z2-21z+10

Factor -21 out of -21z.

9z2-21(z)+10

Rewrite -21 as -6 plus -15

9z2+(-6-15)z+10

Apply the distributive property.

9z2-6z-15z+10

9z2-6z-15z+10

Group the first two terms and the last two terms.

(9z2-6z)-15z+10

Factor out the greatest common factor (GCF) from each group.

3z(3z-2)-5(3z-2)

3z(3z-2)-5(3z-2)

Factor the polynomial by factoring out the greatest common factor, 3z-2.

(3z-2)(3z-5)

Factor 9z^2-21z+10