Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Linear Programming

Question:

The equation of tangent line to $y=2x^2+7$ which is parallel to the line $4x-y+3=0$ is :

Options:

$4x-y+1=0$

$4x-y+5=0$

$x+4y+5=0$

$4x-y+3=0$

Correct Answer:

$4x-y+5=0$

Explanation:
$y=2x^2+7$  ...(1)   line $4x-y+3=0$
differentiating wrt x   or $y=4x+3$ as $\frac{dy}{dx}=4$
so $\frac{dy}{dx}=4x=m=4$   slope of line (m) = 4

$⇒x=1$  from (1)

so $y=2×1^2+7=9$ point of contact (1, 9)

equation of tangent = $y-9=4(x-1)$

$y-9=4x-4$

so $4x-y+5=0$