# Derivative- Normal line（急!!!)

我想知...

find the equation for the normal line to F(x) at x=4

係用咩式同有咩step計佢出泥

thx~

### 1 Answer

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- 1 decade agoFavorite Answer
搵normal既話,要先搵slope of tangent

既然我唔知個function係咩,我唯有用F'(x)繼續做落去.

y = F(x)

slope of tangent = F'(x)

As tangent ⊥ normal,

slope of tangent * slope of normal = -1

F'(x) * slope of normal = -1

slope of normal = -1 / F'(x)

slope of normal line to F(x) at x=4 = -1 / F'(4)

Then, the equation for the normal line to F(x) at x=4 is

[ y - F(4) ] / ( x - 4) = -1 / F'(4)

F'(4)y - F(4) F'(4) = - x + 4

x + F'(4)y = F(4) F'(4) + 4 //

Source(s): by My Maths

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