C2 Geometric
Maths and statistics discussion, revision, exam and homework help.
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Re: C2 GeometricWe know the formula is(Original post by Secreay)
In a GP the 2nd term is -12 and the 5th term is 768. Find the common ratio and the first term. how would you do this one?
Sub in -12 and n=2 in the formula, then sub in 768 and n=5, you will get two equations, solve them simultaneously. -
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Re: C2 Geometric(Original post by Secreay)
-12/r = 768/r^4 seems wrong :/
You are going right. -
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Re: C2 Geometricwhy not?(Original post by Secreay)
but i cant cube root i neg number -
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Re: C2 GeometricNegative numbers can be cube rooted but you can't take the square root of them. Input it in your calc, and it will give the answer.(Original post by Secreay)
but i cant cube root i neg number -
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Re: C2 Geometric(Original post by Secreay)
HAHA im a noob so r=-4?
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Re: C2 GeometricThis is how I went around the equation.
You might find this way easier ^^
-12r^-1=768r^-4
-12=768r-4/r^-1
-12=(768/r^4)/(1/r)
-12=(768/r^4)*(r/1) [doing the dividing fractions so flip the right]
-12=768r/r^4 [now apply indices rules here]
-12=768r^-3
-1/64=r^-3
-1/64=1/r^3
-64/1=r^3/1 [flipped top and bottom]
-4=r -
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Re: C2 GeometricI really don't understand, why you quoted me?(Original post by Stickyelmo)
This is how I went around the equation.
You might find this way easier ^^
-12r^-1=768r^-4
-12=768r-4/r^-1
-12=(768/r^4)/(1/r)
-12=(768/r^4)*(r/1) [doing the dividing fractions so flip the right]
-12=768r/r^4 [now apply indices rules here]
-12=768r^-3
-1/64=r^-3
-1/64=1/r^3
-64/1=r^3/1 [flipped top and bottom]
-4=r
Its not a problem for me to deal with such questions and the way i was doing was easier than your's.
![\displaystyle \frac{r^4}r = - \frac{768}{12} \implies r^3 = -64 \implies r = \sqrt[3]{-64} = -4](http://www.thestudentroom.co.uk/latexrender/pictures/06/064d079d184019348ac1968a863c6b65.png "\displaystyle \frac{r^4}r = - \frac{768}{12} \implies r^3 = -64 \implies r = \sqrt[3]{-64} = -4")
Who's method is better? -
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Re: C2 Geometrichis method is better....less booky(Original post by raheem94)
I really don't understand, why you quoted me?
Its not a problem for me to deal with such questions and the way i was doing was easier than your's.
Who's method is better?
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Re: C2 GeometricCorrect, both are the same, but i was surprised to be quoted, may be if the post would have been directed to the OP then it would have made a bit of sense.(Original post by F1Addict)
Both methods are exactly the same.. one looks shorter as a lot of the steps can be done mentally and not written down. -
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Re: C2 Geometric(Original post by raheem94)
Correct, both are the same, but i was surprised to be quoted, may be if the post would have been directed to the OP then it would have made a bit of sense.
"Who's method is better?"
you were asking the question faget
go back to doing questions in the book
