Posted by **Amy** on Saturday, January 12, 2008 at 5:27pm.

I've been trying to figure out this equation for over an hour but all the answers I get are wrong. The equation is 0.9=-10I^2+6I . The answer is supposed to be 0.3 and it does work out, but I have tried all different ways to solve for I and nothing seems to work. Could someone please help me?

- Algebra -
**Damon**, Saturday, January 12, 2008 at 5:45pm
I assume you know how to complete the square

-10 x^2 + 6 x = 0.9

x^2 -.6 x = -0.09

x^2 -.6 x + .09 = -.09+.09 = 0

(x-.3)^2 = 0

x = .3 sure enough.

- Algebra -
**Damon**, Saturday, January 12, 2008 at 5:49pm
x^2 -.6 x = -0.09 or just rearrange and factor

x^2 - .6 x + 0.09 = 0

(x-.3)(x-.3) = 0

x = .3 and x = .3

- Algebra -
**Amy**, Saturday, January 12, 2008 at 5:50pm
oh, I forgot to thank you, so thank you very much!

- Algebra -
**Amy**, Saturday, January 12, 2008 at 5:52pm
oh, that makes it so much easier! Thank you so very much, it all makes sense now! :D

- Algebra -
**Amy**, Saturday, January 12, 2008 at 5:50pm
oh, okay, I see what you're doing. I just have one question, though;why is it that when you get rid of the -10, the 6 is affected by it? I would assume that it would be left alone...

- Algebra -
**Damon**, Saturday, January 12, 2008 at 5:54pm
Or use quadratic equation

-10 x^2 + 6 x = 0.9

-10 x^2 + 6 x -.9 = 0

a = -10

b = 6

c = -.9

x = [-6 +/- sqrt (36-36) ]/-20

=-6/-20

=-3/-10

= 0.3

- Algebra -
**Damon**, Saturday, January 12, 2008 at 5:55pm
I divided both sides of the equation - ALL TERMS by -10

- Algebra -
**Damon**, Saturday, January 12, 2008 at 5:58pm
-10 x^2 + 6 x

---------------

-10

= x^2 -.6 x

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