## anonymous one year ago In the function f(x) = 4(x2 − 6x + ____) + 20, what number belongs in the blank to complete the square?

1. mathstudent55

Take half of the x-term coefficient and square it.

2. mathstudent55

The x-term coefficient is -6. Take half of -6, and square it. What do you get?

3. anonymous

Half of it so like -3?

4. mathstudent55

Yes. Now square it.

5. anonymous

ok its -1.73

6. anonymous

or well - 1.7

7. mathstudent55

Not square root. Square it. $$(-3)^2 = (-3)(-3) = 9$$

8. anonymous

Oh square it XD

9. mathstudent55

$$\sqrt 3 \approx 1.732$$ <----- not this $$(-3)^2 = 9$$ <---- this is what you do

10. anonymous

Ok understood!

11. mathstudent55

The answer is 9. Just so you know, this method (take half of the x-term coefficient and square it) works for completing the square, but it only works when the coefficient of the x^2 term is 1. In your case, you do have x^2 - 6x, so you see that the coefficient of the x^2 term is 1.

12. anonymous

Thanks

13. mathstudent55

You're welcome.