Respuesta :

tonb

Answer:

b = 40

Step-by-step explanation:

You want your discriminant to be zero because then you have exactly one solution.

Solve b²-4ac = 0

=>

b² - 4·400 = 0

b = ±√1600

so b=±40

but f(-20) also has to be 0

so b=40 remains as the solution

Answer:

b = 40

Step-by-step explanation:

If x = - 20 is a zero of f(x) then f(- 20) = 0 , that is

(- 20)² - 20b + 400 = 0

400 - 20b + 400 = 0

800 - 20b = 0 ( subtract 800 from both sides )

- 20b = - 800 ( divide both sides by - 20 )

b = 40

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