Comprehension

Consider the following for the two (02) items that follow:
The slope of the tangent to the curve y = f(x) at (x, f(x) ) is 4 for every real number x and the curve passes through the origin.

What is the nature of the curve?

This question was previously asked in
NDA-I (Mathematics) Official Paper (Held On: 13 Apr, 2025)
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  1. A straight line passing through (1,4)
  2. A straight line passing through (-14)
  3. A parabola with vertex at origin and focus at (2,0)
  4. A parabola with vertex at origin and focus at (1, 0)

Answer (Detailed Solution Below)

Option 1 : A straight line passing through (1,4)
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Detailed Solution

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Calculation:

Given,

The slope of the tangent to the curve y = f(x) at (x, f(x)) is 4 for every real number x , and the curve passes through the origin.

The slope of the tangent is the derivative of the function, so we have:

\( f'(x) = 4 \)

Integrating f'(x) = 4  with respect to  x :

\( f(x) = 4x + C \)

The curve passes through the origin, so when x = 0 , y = 0 . Substituting these values into the equation f(x) = 4x + C :

\( 0 = 4(0) + C \quad \Rightarrow \quad C = 0 \)

Therefore, the equation of the curve is:

\( f(x) = 4x \)

This is the equation of a straight line with a slope of 4, passing through the origin.

 The curve is a straight line with a slope of 4, passing through the origin.

Hence, the correct answer is option 1.

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