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Vector Algebra

Question
CBSEENMA12032799

Draw a rough sketch of the region {(x, y): y2 ≤ 3 x, 3 x2 + 3 y2 ≤ 16} and find the area enclosed by the region using method of integration.

Solution

Given region is
                 open curly brackets left parenthesis straight x comma space straight y right parenthesis space colon space straight y squared less or equal than 3 straight x comma space 3 straight x squared plus 3 straight y squared less or equal than 16 close curly brackets
Consider the equations
                        straight y squared equals 3 space straight x comma space                   ...(1)
              3 straight x squared plus 3 straight y squared space equals space 16
i.e.,     straight x squared plus straight y squared space equals space 16 over 3                      ...(2)
From (1) and (2), we get,
                     straight x squared plus 3 straight x space equals space 16 over 3 space space space or space space 3 straight x squared plus 9 straight x minus 16 space equals space 0
therefore space space straight x space equals space fraction numerator negative 9 plus-or-minus square root of 81 plus 192 end root over denominator 6 end fraction space equals fraction numerator negative 9 plus-or-minus square root of 273 over denominator 6 end fraction
Rejecting negative values of x, we get
straight x equals fraction numerator negative 9 plus square root of 273 over denominator 6 end fraction equals space straight a

which gives the abscissa of the points of intersection P and Q.
Required area  = Area of shaded region
= 2 [area of region APOA]
= 2 [area of region AMPA + area of region MOPM ]
 = 2 open square brackets integral subscript 0 superscript straight a square root of 3 space square root of straight x dx plus space integral subscript straight a superscript 4 divided by square root of 3 end superscript square root of 16 over 3 minus straight x squared end root space dx close square brackets
=  2 square root of 3 open square brackets fraction numerator straight x to the power of 3 divided by 2 end exponent over denominator begin display style 3 over 2 end style end fraction close square brackets subscript 0 superscript straight a plus 2 open square brackets fraction numerator straight x square root of begin display style 16 over 3 end style minus straight x squared end root over denominator 2 end fraction plus fraction numerator begin display style 16 over 3 end style over denominator 2 end fraction sin to the power of negative 1 end exponent open parentheses fraction numerator straight x over denominator 4 divided by square root of 3 end fraction close parentheses close square brackets subscript 0 superscript fraction numerator 4 over denominator square root of 3 end fraction end superscript
equals space fraction numerator 4 over denominator square root of 3 end fraction left parenthesis straight a to the power of 3 divided by 2 end exponent minus 0 right parenthesis space plus space open square brackets open curly brackets 0 plus 16 over 3 sin to the power of negative 1 end exponent left parenthesis 1 right parenthesis close curly brackets minus open curly brackets straight a square root of 16 over 3 minus straight a squared end root plus 16 over 3 sin to the power of negative 1 end exponent open parentheses fraction numerator straight a square root of 3 over denominator 4 end fraction close parentheses close curly brackets close square brackets
equals space fraction numerator 4 over denominator square root of 3 end fraction straight a to the power of 3 divided by 2 end exponent plus 8 over 3 straight pi minus straight a square root of 16 over 3 minus straight a squared end root minus 16 over 3 sin to the power of negative 1 end exponent open parentheses fraction numerator straight a square root of 3 over denominator 4 end fraction close parentheses

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