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Diketahui sudut lancip. Nilai dari adalah...

Diketahui sin space alpha space equals space 1 fifth square root of 13 comma space alpha space sudut lancip. Nilai dari cos space 2 alpha adalah...

  1. -1

  2. negative 1 half

  3. negative 1 fifth

  4. negative 1 over 25

  5. 1

Jawaban:

sin space alpha space equals space 1 fifth square root of 13 comma space alpha space sudut lancip.

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 cos space 2 alpha equals cos squared alpha minus sin squared alpha  A t u r a n space cos i n u s space rightwards arrow cos space 2 alpha equals 1 minus 2 sin squared space alpha  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 cos space 2 alpha equals 2 space cos squared alpha minus 1

cos space 2 alpha equals 1 minus 2 sin squared space alpha equals 1 minus 2 open parentheses 1 fifth square root of 13 close parentheses squared  space space space space space space space space space space space equals 1 minus 2 open parentheses 13 over 25 close parentheses equals fraction numerator 25 minus 26 over denominator 25 end fraction equals negative 1 over 25

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