C1 Questions - Help needed.

Slenderman

2

Thanks all for helping, everything solved. :smile:

(edited 8 years ago)

Reply 1

Dr. Swiftie

8

For the last bit of inequalities, I always sketch a graph with the two x values.
If the original inequality is >0 the values are when the graph goes above the x axis and if the original inequality is <0 the values are when the graph goes under the x axis.

This is because for >0 , the curve is more than 0 and when the curve goes above the x axis, it is above y=0, so it is more than 0 and it's the opposite for <0.

Idk if that's clear enough but it's how I learnt it. :smile:

Reply 2

Slenderman

OP

2

Cancel off question 13 (ii) and (iii). Know how to do them, on the second paper.

Reply 3

Slenderman

OP

2

Original post by Dr. Swiftie

For the last bit of inequalities, I always sketch a graph with the two x values.
If the original inequality is >0 the values are when the graph goes above the x axis and if the original inequality is <0 the values are when the graph goes under the x axis.

This is because for >0 , the curve is more than 0 and when the curve goes above the x axis, it is above y=0, so it is more than 0 and it's the opposite for <0.

Idk if that's clear enough but it's how I learnt it. :smile:

Omg yes. Now you clicked something in mind, I remember my teacher telling us that. Thanks.

Reply 4

Kevin De Bruyne

21

Original post by Slenderman

Edit: How do you do the last bit of solving a quadratic inequality? I can get the two numbers but I just can't seem to work out whether they need to be < or >. If ya get what I mean.

Sketch the graph and identify where it is >0 and where it is <0.

Reply 5

liverpool2044

10

for the 13 on the first paper, put it in to one equation and use a quadratic equation to show that there is a positive root

Reply 6

Slenderman

OP

2

Yep I can do it now, thanks.

Reply 7

liverpool2044

10

For 12iii on second what did you get in th a(x+b)^2-c equation?

Reply 8

Slenderman

OP

2

Original post by liverpool2044

for the 13 on the first paper, put it in to one equation and use a quadratic equation to show that there is a positive root

Hmm I see so you use the quadratic formula on it. I will try this now.

Reply 9

Slenderman

OP

2

Original post by liverpool2044

For 12iii on second what did you get in th a(x+b)^2-c equation?

I got 3(x+1)^2 +7

Reply 10

Slenderman

OP

2

Original post by liverpool2044

for the 13 on the first paper, put it in to one equation and use a quadratic equation to show that there is a positive root

I used b^2 - 4ac and got k +/- square root k^2 + 8

Now what?

Reply 11

liverpool2044

10

Original post by Slenderman

I got 3(x+1)^2 +7

Good, so you know the minimum point is going to have y coordinate 7 so its always going to be above the x axis

Reply 12

Slenderman

OP

2

I see, that's so simple. The way they worded it made me confused. Thanks.

Reply 13

liverpool2044

10

Original post by Slenderman

I used b^2 - 4ac and got k +/- square root k^2 + 8

Now what?

you know its going to have to be greater than 0 so put it into the quadratic formula so it applies to all values for k

Reply 14

Slenderman

OP

2

Original post by liverpool2044

you know its going to have to be greater than 0 so put it into the quadratic formula so it applies to all values for k

Okay. So I got.. the same thing over 2. (I used b +/- square root b^2-4ac all over 2). Is this right so far?

Reply 15

liverpool2044

10

k+ root k^2-8 is greater than or equal to zero for all values of k is what you need to say. This shows a positive root for x^2 and so an intersection.