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 one year ago
I'm having trouble doing this question...
(3K5)x^2+Kx+1=0
For what value of K will this quadratic equation have no real roots, one real root, or two real roots?
Answer as an inequality if necessary.
 one year ago
I'm having trouble doing this question... (3K5)x^2+Kx+1=0 For what value of K will this quadratic equation have no real roots, one real root, or two real roots? Answer as an inequality if necessary.

This Question is Closed

ZeHanz
 one year ago
Best ResponseYou've already chosen the best response.1This is a quadratic equation: ax²+bx+c=0. The discriminant, D=b²4ac tells you about the number of real roots: D > 0: 2 real roots, D = 0: 1 real root, D < 0, no real roots. You probably know all this already ;) You just have to see that in your own equation a=3K4, b=K and c=1. Put these values for a, b and c in the formula for D and solve the above three cases for K.

tilt
 one year ago
Best ResponseYou've already chosen the best response.1That's as far as I went. As i was solving for no real roots i got stuck at this: dw:1359306176821:dw

phi
 one year ago
Best ResponseYou've already chosen the best response.1what you get is (k2)(k10) < 0 this expression is less than 0 if it is negative. it is negative if one of the factors is + and the other is negative

phi
 one year ago
Best ResponseYou've already chosen the best response.1so you try (k2)< 0 and k10>0 > k<2 and k>10 can not happen or k2 > 0 and k10 < 0 > k>2 and k<10 or 2 < k < 10

tilt
 one year ago
Best ResponseYou've already chosen the best response.1whoa whoa whoa where did you (k2)(k10) from?

phi
 one year ago
Best ResponseYou've already chosen the best response.1k^2 12k+20 < 0 factor into (k2)(k10) < 0

ZeHanz
 one year ago
Best ResponseYou've already chosen the best response.1First, you get: K²12K+20<0 This is the same as (K2)(K10)<0. It equals 0 if K = 2 or K=10. For other values of K it will be positive or negative. If you try K=0 (very simple to do), you get a positive number. To get a negative outcome, you therefore have to have 2<k<10, instead of a number beteen 2 and 10.

tilt
 one year ago
Best ResponseYou've already chosen the best response.1Wait lemme try the other 2 first.

phi
 one year ago
Best ResponseYou've already chosen the best response.1You used "completing the square" to find the roots of K²12K+20=0 you got k=2 and k= 10 which implies k2=0 and k10= 0 this means you could write the quadratic as (k2)(k10) (in case you could not factor the quadratic)

tilt
 one year ago
Best ResponseYou've already chosen the best response.1NOW I am confused. dw:1359306861746:dw

phi
 one year ago
Best ResponseYou've already chosen the best response.1there are two k values that result in 1 real root (a "repeated" root)

tilt
 one year ago
Best ResponseYou've already chosen the best response.1Then they are both answers? Shouldn't be happening though.

phi
 one year ago
Best ResponseYou've already chosen the best response.1Don't get confused. There are two k values that result in a quadratic: x^2+2x+1 =0 5x^2 +10x +1 =0 each has one 1 (repeated) root.

tilt
 one year ago
Best ResponseYou've already chosen the best response.1Then do I put 2 or 10 for the answer?

phi
 one year ago
Best ResponseYou've already chosen the best response.1For what value of K will this quadratic equation have one real root? K=2 or K=10

tilt
 one year ago
Best ResponseYou've already chosen the best response.1Wait let me try the third and last one.

tilt
 one year ago
Best ResponseYou've already chosen the best response.1dw:1359307404608:dw dw:1359307505574:dw

phi
 one year ago
Best ResponseYou've already chosen the best response.1we use the same idea (k2)(k10) > 0 > 0 means the expression is positive (things that are positive are > 0) to be +, both terms must be + or both terms must be  let's first do both positive: k2>0 and k10>0 > k>2 and k>10 both conditions have to be true, so k>10 is the answer now both terms are  k2<0 and k10<0 > k<2 and k<10 Both must be true, so k<2 works

tilt
 one year ago
Best ResponseYou've already chosen the best response.1So you take the bigger one of the two and forge an equation from the two?

phi
 one year ago
Best ResponseYou've already chosen the best response.1ask again, I don't understand the question.

tilt
 one year ago
Best ResponseYou've already chosen the best response.1So I take the bigger inequalities from both the positive and the negative trials and put them together? Like take the bigger one from k>2 / k>10 and k<2 / k<10? In which case 2>k>10?

phi
 one year ago
Best ResponseYou've already chosen the best response.1I would not write it 2>k>10 (you only use this notation if k is between 2 and 10) in this case k<2 results in quadratics with 2 real roots and k>10 results in quadratics with 2 real roots I would say For what value of K will this quadratic equation have 2 real roots? for K<2 or k>10

tilt
 one year ago
Best ResponseYou've already chosen the best response.1Ohhh. So I don't clump them together. The only time when I do is if I am solving for when there aren't any real roots. Anyways, so I take the bigger inequalities from the above question for my answer?

tilt
 one year ago
Best ResponseYou've already chosen the best response.1I am still wondering how you chose the inequalities.

phi
 one year ago
Best ResponseYou've already chosen the best response.1so I take the bigger inequalities ? 1 step at a time: (k2)(k10) > 0 this is the condition for 2 real roots You agree that this means (k2)(k10) is positive (almost by definition) ?

tilt
 one year ago
Best ResponseYou've already chosen the best response.1No, I mean like for K>2 K>10 and K<2 and K<10. How did you choose 2 of them? Can't you also choose k<10 and k>2?

phi
 one year ago
Best ResponseYou've already chosen the best response.1Yes, I understand the question, and it will take a few simple sentences to explain. But the first question is (k2)(k10) > 0 this is the condition for 2 real roots You agree that this means (k2)(k10) is positive (almost by definition) ?

tilt
 one year ago
Best ResponseYou've already chosen the best response.1Yeah. The discriminant must be positive for 2 real roots.

phi
 one year ago
Best ResponseYou've already chosen the best response.1(k2)(k10) > 0 this means that both (k2) is positive and (k10) is positive or k2 > 0 and at the same time k10>0 or k>2 and at the same time k>10 obviously k=3 would make the (k2) positive, but the (k10) term would be negative. We need both to be positive. so if you need k>2 and k>10, k>10 works for both terms i.e. k2 will be positive and k10 will be positive. Does that answer the question ?

phi
 one year ago
Best ResponseYou've already chosen the best response.1Similarly, both terms could be negative, resulting in their product being positive.

tilt
 one year ago
Best ResponseYou've already chosen the best response.1I got it, but where did you get the other one from. I got k>10. How about the k<2?

precal
 one year ago
Best ResponseYou've already chosen the best response.0dw:1359309274367:dw no solution is where your quadratic function does not cross the x axis

phi
 one year ago
Best ResponseYou've already chosen the best response.1try doing the analysis with both terms being negative (  *  = +)

phi
 one year ago
Best ResponseYou've already chosen the best response.1(k2)(k10) > 0 this could happen if (k2) is negative and (k10) is negative

precal
 one year ago
Best ResponseYou've already chosen the best response.0remember the number of times the function crosses the x axis is the number of solutions otherwise you are on the correct path, just reminding you about you are looking for Listen to phi

tilt
 one year ago
Best ResponseYou've already chosen the best response.1Yes, so it can also be k<2 and k<10. k<10 works for both too though.

tilt
 one year ago
Best ResponseYou've already chosen the best response.1Surely it can't be k<10 and k>10

tilt
 one year ago
Best ResponseYou've already chosen the best response.1Getting mixed up with negatives... I got it now. So k<2 also works for k<10

phi
 one year ago
Best ResponseYou've already chosen the best response.1yes. I draw a number line, and arrows. the place where I get 2 lines overlapping is the answer so for k<2 and k<10 I would draw dw:1359309685962:dw

phi
 one year ago
Best ResponseYou've already chosen the best response.1or do lots of problems, in which case you memorize the different cases.

tilt
 one year ago
Best ResponseYou've already chosen the best response.1I know how to solve these questions easily... it's just that the teacher decided to stump the class... :(

tilt
 one year ago
Best ResponseYou've already chosen the best response.1Thanks lol. I got it now :D
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