# maths a level

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#1
Hi
I am a bit confused

when you have an expression such as (3+12x)/x=4 why do you multiply by x^2

and when are the cases when you don't do that
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1 month ago
#2
Why would you multiply by x^2. Multiply both sides by x would give you the correct answer.

You would only multiply by x^2 If its an inequality
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1 month ago
#3
(Original post by Sclaremonths)
Hi
I am a bit confused

when you have an expression such as (3+12x)/x=4 why do you multiply by x^2

and when are the cases when you don't do that
You don't do that in this case! If you multiply that equation by x^2 then you will introduce the spurious solution x = 0 which doesn't satisfy your original equation
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#4
(Original post by Itsmikeysfault)
Why would you multiply by x^2. Multiply both sides by x would give you the correct answer.

You would only multiply by x^2 If its an inequality
ohhh okay thank you so much!
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#5
(Original post by davros)
You don't do that in this case! If you multiply that equation by x^2 then you will introduce the spurious solution x = 0 which doesn't satisfy your original equation
i also wanted to ask when asked to find the equation of the tangent/normal, why do we sometimes take the negative reciprocal of the gradient, and in other occasions we don't
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1 month ago
#6
(Original post by Sclaremonths)
i also wanted to ask when asked to find the equation of the tangent/normal, why do we sometimes take the negative reciprocal of the gradient, and in other occasions we don't
You only take the negative reciprocal for the normal not for the tangent
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#7
(Original post by LemonCake1234)
You only take the negative reciprocal for the normal not for the tangent
okay thank you!
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1 month ago
#8
(Original post by Sclaremonths)
okay thank you!
No worries ask if you need more help!
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#9
(Original post by LemonCake1234)
No worries ask if you need more help!

Hi,
here we take the negative reciprocal of the gradient despite the question asking for the tangent. Why?
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1 month ago
#10
(Original post by Sclaremonths)

Hi,
here we take the negative reciprocal of the gradient despite the question asking for the tangent. Why?
The gradient is of the centre and point on the circle, so the radius. The tangent’s gradient is perpendicular to the radius, so you take the negative reciprocal.
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1 month ago
#11
(Original post by Sclaremonths)

Hi,
here we take the negative reciprocal of the gradient despite the question asking for the tangent. Why?
You take the negative reciprocal when ever you want something that is perpendicular
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#12
The gradient is of the centre and point on the circle, so the radius. The tangent’s gradient is perpendicular to the radius, so you take the negative reciprocal.
and in the instance that they are asking for the normal?
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