margot Posted January 27, 2006 Share Posted January 27, 2006 "Is each question a direct variation? If it is, what is the constant of variation?" y = 5 over 3 x TT;; I don't get it at all.. Link to comment

Kreutz Posted January 27, 2006 Share Posted January 27, 2006 It's been a while since I had Algebra, but that doesn't sound like direct variation to me. Link to comment

margot Posted January 27, 2006 Author Share Posted January 27, 2006 TT...can someone tell me how to figure that out???? Link to comment

Kreutz Posted January 27, 2006 Share Posted January 27, 2006 Well, direct variation would be something like y=mx, where m is a constant. That is to say, a change in y would result in a direct change in x. If that x had been on the outside, 5/3 would have been a constant. Even if you solve for x and determine y, y is still in a fraction. So, my vote goes to no. Link to comment

margot Posted January 27, 2006 Author Share Posted January 27, 2006 whatt I don't get it at all..>> Link to comment

Kreutz Posted January 27, 2006 Share Posted January 27, 2006 OK, then think about the graph of the function. y=3x would produce a straight line. y=(5/3)x would also produce a straight line. y=5/3x would produce a parabolic function (or whatever the hell that double-curve thing in quadrants I and III is, someone besides Lindsay can tell me). Therefore, since the line isn't straight, the variation isn't direct. Link to comment

margot Posted January 27, 2006 Author Share Posted January 27, 2006 like... y = 2x + 4 and I know the answer is that it is not a direct variation (the back of the book says so) but how would I know? Link to comment

stranger Posted January 27, 2006 Share Posted January 27, 2006 you graph it, and see if the line is linear or not Link to comment

margot Posted January 27, 2006 Author Share Posted January 27, 2006 how would I graph y = 2x + 4 ? Link to comment

stranger Posted January 27, 2006 Share Posted January 27, 2006 hmmm, y=2x+4 is a linear line... in which case it should be a direct variation.... unless it's the 4 that throws everything off... I really don't know how to explain this, partly because i'm not sure myself. Direct variation is when 2 variables, in your y=2x+1 example, they would be y and x, well.. it's when they have a constant ratio. Meaning.. as y changes, then x changes in proportion to y Hmmm.. sorry, I don't think I can help, I haven't taken Algebra in a while.. Hope you could figure it out though EDIT: After more thought, y=2x+4 should definitely be a direct variation... because 2 acts as the constant, and when y doubles (or tripes, or whatever) then so does x... What am I missing? Link to comment

Arcane Posted January 27, 2006 Share Posted January 27, 2006 A direct variation equation has to pass through the origin (0,0). So y = 2x + 4 is not a direct variation because it does not passes through the origin, it pass through (0,4). A direct variation equation must be in the form of y = kx, where k is a constant. y = kx + b is not a direct variation. Link to comment

David Posted January 27, 2006 Share Posted January 27, 2006 Direct Variation follows the formula y = kx. Y is Y, X is X, and K is the variation constant. y = 3x, Direct Variation, K = 3 y = 3x + 2, NOT Direct Variation 4y = 6x, y = 6x/4, Direct Variation, K = 6/4 = 3/2 = 1.5 4y = 6x + 9, y = 6x/4 + 9/4, NOT Direct Variation Got it? Link to comment

margot Posted January 27, 2006 Author Share Posted January 27, 2006 wait how do i solve this y = 2x + 4 ?? Link to comment

Kreutz Posted January 27, 2006 Share Posted January 27, 2006 wait how do i solve this y = 2x + 4 ?? It is solved, for y. To solve it for a value, insert the value (i.e. for x=2, then it would be y=2(2)+4=8). To solve it for x, subtract the four from both sides and then divide both sides by 2. To graph it, plot a line with a slope of 2 which intersects the y-axis at y=4. Link to comment

margot Posted February 2, 2006 Author Share Posted February 2, 2006 How do you convert slope intercept form (y = mx+b) to standard form?? (Ax + By = C) Link to comment

margot Posted February 2, 2006 Author Share Posted February 2, 2006 also, what the hell???? "find the slope of a line parallel to the graph of each equation." y = 1/2x + 2.3 Link to comment

Kreutz Posted February 2, 2006 Share Posted February 2, 2006 How do you convert slope intercept form (y = mx+b) to standard form?? (Ax + By = C) Man, that's ancient. I haven't seen 'standard form' in a long time. I don't even remember anymore. also, what the hell???? "find the slope of a line parallel to the graph of each equation." y = 1/2x + 2.3 Well, it seems to me that a line parallel to any graph would share it's slope. Maybe it's a trap! Link to comment

Alundra Posted February 2, 2006 Share Posted February 2, 2006 Now I remember why I failed Algebra and took it over the summer Freshman year of HS. Link to comment

margot Posted February 2, 2006 Author Share Posted February 2, 2006 woah guys, I actually figured out the paralell line thing ON MY OWN. (please post applause .gifs kreutz.) Link to comment

Arcane Posted February 2, 2006 Share Posted February 2, 2006 How do you convert slope intercept form (y = mx+b) to standard form?? (Ax + By = C) Just get the x and y variables on the left side of the equation. For example, with the y = (1/2)x + 2.3 equation, all you would need to do is subtract the (1/2)x from both sides to give you -(1/2)x + y = 2.3. Remember that A, B, and C are just constants, so all you really have to worry about when getting an equation into standard form is getting both the x and the y on the left side of the equation. In that last example, A = -1/2, B = 1, and C = 2.3. Link to comment

Kreutz Posted February 3, 2006 Share Posted February 3, 2006 woah guys, I actually figured out the paralell line thing ON MY OWN. (please post applause .gifs kreutz.) ...Ok, you deserve it. Link to comment

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