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Vector Algebra

Question
CBSEENMA12032808

Find the whole area of the circle x2 + y2 = a2.

Solution
The equation of circle is x2 + y2 = a2     ...(1)
Its centre is origin and radius a. We know that circle x2 + y2 = a2 is symmetrical about both axes.
therefore space space space required space area space equals space 4 space integral subscript 0 superscript straight a straight y space dx space equals space 4 space integral subscript 0 superscript straight a square root of straight a squared minus straight x squared end root space dx
                  equals space 4 open square brackets fraction numerator straight x square root of straight a squared minus straight x squared end root over denominator 2 end fraction plus straight a squared over 2 sin to the power of negative 1 end exponent straight x over straight a close square brackets subscript 0 superscript straight a
equals space 4 open square brackets open parentheses 0 plus straight a squared over 2 sin to the power of negative 1 end exponent 1 close parentheses space minus space open parentheses 0 plus straight a squared over 2 sin to the power of negative 1 end exponent 0 close parentheses close square brackets
equals space 4 open square brackets open parentheses 0 plus straight a squared over 2 sin to the power of negative 1 end exponent 1 close parentheses space minus space open parentheses 0 plus straight a squared over 2 sin to the power of negative 1 end exponent 0 close parentheses close square brackets
equals 4 space open square brackets straight a squared over 2 cross times straight pi over 2 close square brackets space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space sin to the power of negative 1 end exponent 0 space equals space 0 close square brackets
space equals space straight pi space straight a space.


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