Question

Find the exact value of tan(x-y) if sin x=8/17 cosy = 3/5

Answer 1

To solve the the question we proceed as follows:

From trigonometric laws

$(cos x)^2+(sin x)^2=1$

$(cos x)^2+(sin x)^2=1$

$sin (x-y)=sin$ $x$ $sin$ $y-sin$ $y$ $cos$ $x$

$cos (x-y)=cos$ $x$ $cos$ $y+sin$ $x$ $xin$ $y$

si  $x=\frac{8}{17}$

$cos$ $x=sqrt(1-(sin x)^2)=sqrt(1-64/289)=sqrt(\frac{225}{289} )=\frac{15}{17}$

$cos$ $y=\frac{3}{5}$

$sin$ $x= sqrt(1- (cos x)^2)= sqrt(1-\frac{9}{25} )=sqrt(\frac{16}{25} )=\frac{4}{5}$

thus

$tan (x-y)=[sin (x-y)]/[cos (x-y)]$

=[sin x cos y-sin y cos x]/[cos x cos y+sin x sin y]

plugging in the values we obtain:

$[8/17 *3/5-4/5*15/7]/[15/17*3/5+8/17*4/5]$

simplifying

$[24/85-60/85]/[45/85+32/85]$

$=-\frac{36}{77}$