Core 1 maths question

Watch this thread
ruby_zara
Badges: 9
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#1
Report Thread starter 5 years ago
#1
Hi, please could someone help me with the last part of this question. I don't quite understand from the mark scheme how you get to the answer. I'll just put the other parts of the question in before for context.
In the previous parts of the question you have to complete the square on 2x^2+6x+5 which I unmderstand and then write down the minimum value for the second part, which would be 1/2.

And then it says if point A has co-ordinates (-3,5) and point B has the co-ordinates (x,3x+9) show that AB^2 = 5(2x^2 +6x +5), which I understand how to do but then the last part says
Using your answer from part a).ii (which was 1/2) find the minimum value of the length AB as x varies giving your answer in the form 1/2(square root of n) where n is an integer.
Sorry if that is really confusing . If it helps the links to the past paper and mark scheme are here.
http://filestore.aqa.org.uk/subjects...1-QP-JUN13.PDF - question paper
http://filestore.aqa.org.uk/subjects...W-MS-JUN13.PDF - mark scheme
Thanks
0
reply
tajtsracc
Badges: 4
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#2
Report 5 years ago
#2
(Original post by ruby_zara)
Hi, please could someone help me with the last part of this question. I don't quite understand from the mark scheme how you get to the answer. I'll just put the other parts of the question in before for context.
In the previous parts of the question you have to complete the square on 2x^2+6x+5 which I unmderstand and then write down the minimum value for the second part, which would be 1/2.

And then it says if point A has co-ordinates (-3,5) and point B has the co-ordinates (x,3x+9) show that AB^2 = 5(2x^2 +6x +5), which I understand how to do but then the last part says
Using your answer from part a).ii (which was 1/2) find the minimum value of the length AB as x varies giving your answer in the form 1/2(square root of n) where n is an integer.
Sorry if that is really confusing . If it helps the links to the past paper and mark scheme are here.
http://filestore.aqa.org.uk/subjects...1-QP-JUN13.PDF - question paper
http://filestore.aqa.org.uk/subjects...W-MS-JUN13.PDF - mark scheme
Thanks
The minimum value for 2x2 + 6x + 5 is 1/2, hence the minimum point for AB2 is equal to 5 times the minimum value of 2x2 + 6x + 5 (which is a 1/2), hence 5 x 1/2 = 5/2.

But they wanted the minimum value of AB, not (AB)2, so square root this value. √5/2

√5/2 = √5/√2 Now rationalise the denominator. √5 x √2 / √2 x √2 = √10/2 = 1/2√10.
1
reply
ruby_zara
Badges: 9
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#3
Report Thread starter 5 years ago
#3
(Original post by tajtsracc)
The minimum value for 2x2 + 6x + 5 is 1/2, hence the minimum point for AB2 is equal to 5 times the minimum value of 2x2 + 6x + 5 (which is a 1/2), hence 5 x 1/2 = 5/2.

But they wanted the minimum value of AB, not (AB)2, so square root this value. √5/2

√5/2 = √5/√2 Now rationalise the denominator. √5 x √2 / √2 x √2 = √10/2 = 1/2√10.
Thank you so much
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

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

Personalise

Y13's - If you haven't confirmed your firm and insurance choices yet, why is that?

I am waiting until the deadline in case anything in my life changes (23)
20.35%
I am waiting until the deadline in case something else changes (e.g. exams/pandemic related concerns) (12)
10.62%
I am waiting until I can see the unis in person (8)
7.08%
I still have more questions before I make my decision (19)
16.81%
No reason, just haven't entered it yet (28)
24.78%
Something else (let us know in the thread!) (23)
20.35%

Watched Threads

View All