What is the slope of the line normal to the tangent line of #f(x) = 2x^2-xsqrt(x^2-x) # at # x= 2 #?

1 Answer
Feb 9, 2017

#"The Reqd. Slope="(16+5sqrt2)/103#.

Explanation:

Recall that, #f'(2)# gives the slope of the Tangent Line to the

Curve C : #y=f(x)=2x^2-xsqrt(x^2-x)#

at the pt. #P(2,f(2))=P(2,8-2sqrt2)#.

As Normal at pt. #P# is #bot# to the tgt., its slope is given by,

#1/(f'(2)), if f'(2)!=0#.

Now, #f(x)=2x^2-xsqrt(x^2-x) = 2x^2-sqrt(x^4-x^3).#

#:. f'(x)=2(2x)-1/(2sqrt(x^4-x^3))*(x^4-x^3)'#

#=4x-1/(2sqrt(x^4-x^3))*(4x^3-3x^2)#

#=4x-(x^2(4x-3))/(2xsqrt(x^2-x))#

#:. f'(x)=4x-(x(4x-3))/(2sqrt(x^2-x))#

#rArr f'(2)=8-(2(8-3))/(2sqrt(4-2))=8-5/sqrt2=(8sqrt2-5)/sqrt2 !=0.#

Hence, the Reqd. Slope #=sqrt2/(8sqrt2-5)=(sqrt2(8sqrt2+5))/{(8sqrt2)^2-5^2}#

#=(16+5sqrt2)/103#.