Diketahui tan a 12/5 dan sin b=4/5,a dan b sudut lancip tent nilai cos (a-b)....

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fungsi trigonometri

tan a = 12/5= y/x
r=√(x²+y²) = 13
sin a = y/r = 12/13
cos a = x/r = 5/13

sin b = 4/5
cos b = √(1- sin² b) = 3/5

cos (a - b) = cos a cos b + sin a sin b
cos (a-b) = (5/13 x 3/5) + (12/13 x 4/5) =15/65 + 48/65 = 63/65