# Maths Question Help

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#1
Guys, I need help on this question. So far I've got:
4.9t^2 -13.2t+6<0
4.9t^2-13t+6.3<0
Last edited by Nithu05; 2 months ago
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2 months ago
#2
Think you need to check your constant terms.
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#3
(Original post by mqb2766)
Think you need to check your constant terms.
Well, they're both projected from different heights so I added 4 onto the initial heights but now that I think about it, I think you need to subtract 4 from the heights? However, even if I do this I'll end up with two quadratics. How am I supposed to solve them simultaneously? Am I supposed to work out the inequalities separately and then combine them?
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2 months ago
#4
(Original post by Nithu05)
Well, they're both projected from different heights so I added 4 onto the initial heights but now that I think about it, I think you need to subtract 4 from the heights? However, even if I do this I'll end up with two quadratics. How am I supposed to solve them simultaneously? Am I supposed to work out the inequalities separately and then combine them?
Rather than guessing what to do, write each quadratic inequality out fully, then collect terms.
As a fall back working them out seperately then combining will give a solution. It is only a couple of quadratics, should just take a couple of mins.
Last edited by mqb2766; 2 months ago
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#5
(Original post by mqb2766)
Rather than guessing what to do, write each quadratic inequality out fully, then collect terms.
As a fall back working them out seperately then combining will give a solution. It is only a couple of quadratics, should just take a couple of mins.
Ok, so far I got:
4.9t^2-13t+1.7<=0
4.9t^2-13.2t+2<=0
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#6
(Original post by Nithu05)
Ok, so far I got:
4.9t^2-13t+1.7<=0
4.9t^2-13.2t+2<=0
Thing is when I'm working out the roots, they're not whole numbers so something seems wrong.
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2 months ago
#7
(Original post by Nithu05)
Ok, so far I got:
4.9t^2-13t+1.7<=0
4.9t^2-13.2t+2<=0
that looks better, so just solve each of them.
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2 months ago
#8
(Original post by Nithu05)
Thing is when I'm working out the roots, they're not whole numbers so something seems wrong.
It doesn't look like a particularly "nice" problem in that respect.
https://www.desmos.com/calculator/s5sbdhrsaa
The quadratics numbers are too close, as you can see from the graphs.

You can always verify by subbing the times back into the original quadratics.
Last edited by mqb2766; 2 months ago
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#9
(Original post by mqb2766)
It doesn't look like a particularly "nice" problem in that respect.
https://www.desmos.com/calculator/s5sbdhrsaa
The quadratics numbers are too close, as you can see from the graphs.

You can always verify by subbing the times back into the original quadratics.
OK, I worked out the combined inequality and got:
0.1611559962<=t<=2.515119982
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#10
(Original post by Nithu05)
OK, I worked out the combined inequality and got:
0.1611559962<=t<=2.515119982
So is this the answer or is there one more step? Thanks so much for your help so far!
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2 months ago
#11
(Original post by Nithu05)
OK, I worked out the combined inequality and got:
0.1611559962<=t<=2.515119982
Possibly a bit too precise for quoting, but just sub back into the quadratics to verify if you want.
They look about right from desmos.
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#12
(Original post by mqb2766)
Possibly a bit too precise for quoting, but just sub back into the quadratics to verify if you want.
They look about right from desmos.
Ok I've substituted the values and it satisfies the inequalities. Should I just leave my answer as this?
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2 months ago
#13
(Original post by Nithu05)
Ok I've substituted the values and it satisfies the inequalities. Should I just leave my answer as this?
Probably not quite that precise (maybe 2 or 3 dp), but yes;
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#14
(Original post by mqb2766)
Probably not quite that precise (maybe 2 or 3 dp), but yes;
Ok thanks so much for your help
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