If you know how to complete a square please help!

In the function f(x) = 5(x^2 - 4x __) + 15, what number belongs in the blank to complete the square?

Question

If you know how to complete a square please help! 

In the function f(x) = 5(x^2 - 4x __) + 15, what number belongs in the blank to complete the square?

anonymous · Answer

x2−4x+?

(b/2)
(-4/2)^2
= +4
x^2-4x+4
The answer would be 4.

anonymous · Answer

Thank you so much!

anonymous · Answer

ur welcome medal plz?

anonymous · Answer

thx

jhonyy9 · Answer

@clanger555 can you prove it your answer please that is right ?

anonymous · Answer

sure

jhonyy9 · Answer

thank you in advance

anonymous · Answer

x2−4x+?

(b/2)
(-4/2)^2
= +4
x^2-4x+4
The answer would be 4.

jhonyy9 · Answer

step by step please - i dont understand it so

jhonyy9 · Answer

f(x) = 5(x^2 - 4x __) + 15

how you make from these a square perfect ?

anonymous · Answer

@clanger555 Could you help with another one?

jhonyy9 · Answer

just bc. this is the exercise ,the question

anonymous · Answer

Thank you so much!