Probability
Full Member
- Joined
- Jan 26, 2012
- Messages
- 425
I have; 3x^2 + 18x + 15. I end up with 3(x+3)^2 - 12. I understand how I did this and don't need any help getting through to the end as shown.
Now what I am asking help with is the reverse of the above.
This is the final line of completing the square; 3(x + 1)^2 - 12
If I expand the brackets and simplify I end up with; x + 3x - 11
I have a graphics calculator and when I enter; 3(x + 1)^2 - 12 the y intercept when x=0 is - 9 and not - 11 as shown?
My working out;
3(x + 1)^2 - 12
3(x + 1)(x + 1) - 12
3(x^2 + x + x + 1) - 12
3(x^2 + 2x + 1) - 12
3x^2 + 6x + 3 - 36
3x^2 + 6x - 33
x^2 + 3x - 11
If my graphic calculator is right could somebody please point out where I am going wrong!
Thanks
Now what I am asking help with is the reverse of the above.
This is the final line of completing the square; 3(x + 1)^2 - 12
If I expand the brackets and simplify I end up with; x + 3x - 11
I have a graphics calculator and when I enter; 3(x + 1)^2 - 12 the y intercept when x=0 is - 9 and not - 11 as shown?
My working out;
3(x + 1)^2 - 12
3(x + 1)(x + 1) - 12
3(x^2 + x + x + 1) - 12
3(x^2 + 2x + 1) - 12
3x^2 + 6x + 3 - 36
3x^2 + 6x - 33
x^2 + 3x - 11
If my graphic calculator is right could somebody please point out where I am going wrong!
Thanks