3. The curve \( y = f(x) \) and the line \( y = -3 \), shown in the figure above, intersect at the points \( (0, -3) \), \( (a, -3) \), and \( (b, -3) \). The sum of area of the shaded region enclosed by the curve and the line is given by:






Answer is: option3

\( \int_0^a [f(x) + 3]\, dx + \int_a^b [-3 - f(x)]\, dx \)

Solution:

Given:

  • The curve \( y = f(x) \) intersects the line \( y = -3 \) at points \( (0, -3) \), \( (a, -3) \), and \( (b, -3) \).
  • Between \( x = 0 \) and \( x = a \), \( f(x) > -3 \).
  • Between \( x = a \) and \( x = b \), \( -3 > f(x) \).

Step-by-Step Solution:

  1. Area between \( x = 0 \) and \( x = a \):
    • Here, \( f(x) \) is above \( y = -3 \), so the height of the region is \( f(x) - (-3) = f(x) + 3 \).
    • The area is:
      \( \int_0^a [f(x) - (-3)]\, dx = \int_0^a [f(x) + 3]\, dx \)
  2. Area between \( x = a \) and \( x = b \):
    • Here, \( y = -3 \) is above \( f(x) \), so the height of the region is \( -3 - f(x) \).
    • The area is:
      \( \int_a^b [-3 - f(x)]\, dx \)
  3. Total Area:
    • The sum of the two areas is:
      \( \int_0^a [f(x) + 3]\, dx + \int_a^b [-3 - f(x)]\, dx \)

Matching with Options:

  • Option (C) matches exactly with the derived expression:
    \( \int_0^a [f(x) + 3]\, dx + \int_a^b [-3 - f(x)]\, dx \)

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