louise18152
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#1
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can someone help me with a alevel maths question
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Smouncher
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#2
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I can try, what is it?
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potatohouse
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well what is it
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louise18152
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#4
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oh sorry triangle abc bc is 12 and cos aBc is 2/3 ac is 2cm bigger then ab
find the length od ab and ac
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ThiagoBrigido
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(Original post by louise18152)
oh sorry triangle abc bc is 12 and cos aBc is 2/3 ac is 2cm bigger then ab
find the length od ab and ac
What have you attempted?
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louise18152
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yea i know what you do with the cos=2/3
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louise18152
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i mean i don't know what you do with the cos
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mqb2766
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(Original post by louise18152)
i mean i don't know what you do with the cos
Try using the cos rule for a triangle.
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laurawatt
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(Original post by louise18152)
i mean i don't know what you do with the cos
Cosine rule is what immediately jumps out at me (assuming the triangle is non-right angled?)
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louise18152
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yeah not right angle
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louise18152
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(Original post by louise18152)
yeah not right angle
i still dont understand
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mqb2766
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(Original post by louise18152)
i still dont understand
You did the cos rule at gcse?
https://www.mathsisfun.com/algebra/trig-cosine-law.html
Last edited by mqb2766; 1 month ago
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louise18152
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no
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potatohouse
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let AB = x and AC = x + 2

Use the cosine rule:
cos(A) = (b^2 + c^2 - a^2)/2bc

let A = 2/3 (make sure its in radians)
a = x+2
b = x
c = 12

So:
cos(2/3)= (x^2 + 12^2 - (x+2)^2)/(2 x x^2 x 12^2)

x = (70)/ (12 cos(2/3) + 1)

is what i got aka 5.345
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mqb2766
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(Original post by louise18152)
no
It's in the syllabus. See link on previous post.
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louise18152
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oh ok thank you
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louise18152
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#17
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(Original post by potatohouse)
let AB = x and AC = x + 2

Use the cosine rule:
cos(A) = (b^2 + c^2 - a^2)/2bc

let A = 2/3 (make sure its in radians)
a = x+2
b = x
c = 12

So:
cos(2/3)= (x^2 + 12^2 - (x+2)^2)/(2 x x^2 x 12^2)

x = (70)/ (12 cos(2/3) + 1)

is what i got aka 5.345
thank you
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louise18152
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#18
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(Original post by potatohouse)
let AB = x and AC = x + 2

Use the cosine rule:
cos(A) = (b^2 + c^2 - a^2)/2bc

let A = 2/3 (make sure its in radians)
a = x+2
b = x
c = 12

So:
cos(2/3)= (x^2 + 12^2 - (x+2)^2)/(2 x x^2 x 12^2)

x = (70)/ (12 cos(2/3) + 1)

is what i got aka 5.345
why did you square the second part?
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potatohouse
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#19
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#19
(Original post by louise18152)
why did you square the second part?
I did not mean to square the c^2 (the number 12) that was a mistake on my part
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