My Math Forum These equations are driving me to insanity!

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 August 22nd, 2010, 02:45 PM #1 Newbie   Joined: Aug 2010 Posts: 3 Thanks: 0 These equations are driving me to insanity! Here is the first one: x2 ?5x =0 Looking at this equation, I assumed it was a quadratic because there is an = 0 sign at the end. But quadratics have the form 'xsquared + bx + c = 0'. I cannot find a solution to this question. Here is the other one: x +3 ? 1/x = 0 Same thing here - absolutely baffled. Somebody please help - I'm loading my shotgun as we speak!
 August 22nd, 2010, 02:53 PM #2 Global Moderator     Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,767 Thanks: 1017 Math Focus: Elementary mathematics and beyond Re: These equations are driving me to insanity! x^2 - 5x = 0, x(x - 5) = 0, x = 5, x = 0. x + 3 - 1/x = 0, multiply both sides by x, x^2 + 3x -1 = 0, x = (-3 ± ?(13))/2.
 August 22nd, 2010, 03:35 PM #3 Senior Member     Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,155 Thanks: 465 Math Focus: Calculus/ODEs Re: These equations are driving me to insanity! You were right, the first one is quadratic, c = 0. In the general form ax˛ + bx + c "b" and "c" can be zero, but "a" cannot.
August 22nd, 2010, 05:42 PM   #4
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Re: These equations are driving me to insanity!

Quote:
 Originally Posted by greg1313 x^2 - 5x = 0, x(x - 5) = 0, x = 5, x = 0. x + 3 - 1/x = 0, multiply both sides by x, x^2 + 3x -1 = 0, x = (-3 ± ?(13))/2.
Thanks for that mate, it really helped.

Bit new to the subject and was having trub getting my head round it.

But to ask for your expertise once again. Can you please help with these ones. The first one is a simultaneous equation - (which i am still new to) and the second is asking me to express x in terms of y

2a - b = 8
3a + 2b = 5

And 'Write out a correct rearrangement of the formula to express x in terms of y'

y =4(x +3) ?2x

 August 22nd, 2010, 05:52 PM #5 Global Moderator     Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,767 Thanks: 1017 Math Focus: Elementary mathematics and beyond Re: These equations are driving me to insanity! First one: [1] 2a - b = 8 [2] 3a + 2b = 5 Multiply [1] by 2: [3] 4a - 2b = 16 Add [2] and [3]: 7a = 21, a = 21/7 = 3. From [1]: 2(3) - b = 8, b = 6 - 8, b = -2. Second one: y = 4(x +3) - 2x y = 4x + 12 - 2x y = 2x + 12 y - 12 = 2x (y - 12)/2 = x.

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