## anonymous 4 years ago how do you complete the square on this 7x^2 + 10x = -2

1. amistre64

2. amistre64

factor out the 7 on the left and work out the square part

3. anonymous

divide by 7 first?

4. amistre64

$7x^2+10x=-2$ $7(x^2+\frac{10}{7}x)=-2$ $7(x^2+\frac{10}{7}x+(\frac{10}{14})^2)=-2+7(\frac{10}{14})^2$

5. amistre64

then I spose we can get rid of that 7 by dividing both sides :)

6. amistre64

$x^2+\frac{10}{7}x+(\frac{10}{14})^2=-\frac{2}{7}+(\frac{10}{14})^2$ compact the left $(x+\frac{10}{14})^2=-\frac{2}{7}+(\frac{10}{14})^2$ and work the rest thru

7. amistre64

yes, divide off the 7 first :)

8. anonymous

i can get to the point where i get (x = (10/14))^2 = 44/196 but dont know what to do after this

9. amistre64

you sqrt the sides to unto the ^2 and add off the 10/14

10. anonymous

11. amistre64

$\sqrt{(x+\frac{10}{14})^2=-\frac{2}{7}+(\frac{10}{14})^2}$ $x+\frac{10}{14}=\pm\sqrt{-\frac{2}{7}+(\frac{10}{14})^2}$ $x=-\frac{10}{14}\pm\sqrt{-\frac{2}{7}+(\frac{10}{14})^2}$

12. anonymous

i mean (-5 + sqrt11)/14

13. amistre64

the sqrt has 2 parts to it a + and a - that has to be accounted for

14. amistre64

x^2 = 4 x = sqrt(4) x = 2, or -2

15. amistre64

heres a simple dbl chk http://www.wolframalpha.com/input/?i=7x%5E2+%2B+10x+%3D+-2

16. amistre64

looks to be a /7 not /14

17. anonymous

ok thanks a mill

18. amistre64

yep