# I don't understand why the discriminant is used here

Watch
Announcements
#1
I don't understand the answer to the question
Last edited by val7322; 1 month ago
0
1 month ago
#2
(Original post by val7322)
I don't understand the answer to the question
For (b) the discriminant tels us information about how many real roots the quadratic has.

discrimant > 0 two real roots; = 0 two equal roots: < 0 no real roots
0
#3
(Original post by Muttley79)
For (b) the discriminant tels us information about how many real roots the quadratic has.

discrimant > 0 two real roots; = 0 two equal roots: < 0 no real roots
but its asking for the range of values for a not for the number of roots?
0
1 month ago
#4
The thing is I don’t understand either. We’re the same bro.
0
1 month ago
#5
(Original post by val7322)
but its asking for the range of values for a not for the number of roots?
You sub the equations together and rearrange which gives you a general equation where a varies.For the graphs to have two points of intersection the general equation found needs to have two roots,thus you use discriminant
0
1 month ago
#6
(Original post by val7322)
but its asking for the range of values for a not for the number of roots?

For (c) put the two equations equal - reaarange into a quadratic then you know the dicriminant must be >0

Do that and post what you get - then we can look at solving the inequality.
Last edited by Muttley79; 1 month ago
0
#7
(Original post by The A.G)
You sub the equations together and rearrange which gives you a general equation where a varies.For the graphs to have two points of intersection the general equation found needs to have two roots,thus you use discriminant
but what does a<-7/16 mean
0
1 month ago
#8
(Original post by val7322)
but what does a<-7/16 mean
It’s the condition that when a is less than -7/16 the graphs will have two points of intersection
0
1 month ago
#9
(Original post by val7322)
but what does a<-7/16 mean
Consider an easier example if you are confused. Consider the curve and the line which is of course just the x-axis. You should be able to see that if a>0 then the curve lies completely above the x-axis so there are no points where the graphs intersect. If a=0 then there is a single (repeated) root. If a<0 then there are two distinct points of intersection.
So if someone told you that the curve crosses the x-axis at two distinct points then you’d have to have a<0.
This is the same as your example, it’s just a bit more complicated.
0
#10
(Original post by B_9710)
Consider an easier example if you are confused. Consider the curve and the line which is of course just the x-axis. You should be able to see that if a>0 then the curve lies completely above the x-axis so there are no points where the graphs intersect. If a=0 then there is a single (repeated) root. If a<0 then there are two distinct points of intersection.
So if someone told you that the curve crosses the x-axis at two distinct points then you’d have to have a<0.
This is the same as your example, it’s just a bit more complicated.
thank you so much, i understand now
0
X

new posts Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### Poll

Join the discussion

#### Would you give consent for uni's to contact your parent/trusted person in a mental health crisis?

Yes - my parent/carer (65)
32.99%
Yes - a trusted person (54)
27.41%
No (52)
26.4%
I'm not sure (26)
13.2%