dik cos a = 1/3, sin b =-1/5 akar 5, brapa nilai tan (a-b)? Mohon Bantuannya Kawan2

cos a = 1/3
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maka 
√(3²-1²)
=√8 = 2√2
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sin a = 2√2 / 3

tan a = 1/2√2
tan a = √2/4
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sin b = -√5/5
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maka
√(5²-5) = √20 = 2√5
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cos b = -2√5 / 5
tan b = 2
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tan(a-b) 
= (tan a - tan b) / (1 + tan a . tan b)
= (√2 /4  -  2) / (1 +  2√2 / 4)
= (√2 - 4) / (4 + 2√2)