Question 237615
z(z-9)=-20

z^2 - 9z = - 20

z^2 - 9z + 20 = 0

What two numbers when multiplied together will yield 20 but when added will yield -9?

How about -4 times -5?

(z - 4)(z - 5) = 0

Set each factor to zero and solve for z individually.


z - 4 = 0

z = 4


z - 5 = 0

z = 5

Solution: z = 4 and z = 5