17 . Let f x
2
( ) ln ( x 4 ) � � .
( a ) Find f� ( x)
.
( b ) Hence , write down the gradient of the tangent to the curve of f at ( 3 , ln13 ) .
It is given that the equation of the normal to the curve of f at ( 3 , ln13 ) is 13x � my � 39 � mln13
, where m is a nonzero constant .
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( c ) Find the exact value of the x -intercept of the normal to the curve of f at ( 3 , ln13 ) .
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