Target Exam

CUET

Subject

-- Mathematics - Section A

Chapter

Applications of Derivatives

Question:

Find the slope of the tangent or normal to given curves at the indicated point as instructed:

y=\( {x }^{ 3} \) at (1,1) : normal

Options:

x+3y-4=0

x+8y-7=0

x-y-4=0

x-y-1=0

Correct Answer:

x+3y-4=0

Explanation:

$y=x^3$

$⇒\frac{dy}{dx}=3x^2$

Slope of normal = $\frac{-1}{dy/dx}=\frac{-1}{3x^2}$

$=\frac{-1}{3}$

$⇒y=mx+C$

$⇒y=\frac{-1}{3}x+C$

$⇒3y=-x+C'$ → satisfied by (1, 1)

$⇒C'=4$

$∴3y=-x+4$