Homework Help: Algebra

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
- Algebra - Amy, Saturday, January 12, 2008 at 6:30pm
  oh, no wonder nothing worked out; thanks!

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