anonymous
  • anonymous
If both x and y are in quadrant IV, and sin x = -2/3 and cos y = 1/4. Find cos (x-y)
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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schrodinger
  • schrodinger
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anonymous
  • anonymous
cosxcosy+sinxsiny
anonymous
  • anonymous
cos( x-y)= cos x cosy+ sinx siny
anonymous
  • anonymous
sin x= -2/3 cox x =sqrt(1 +4/9)=sqrt(13)/3

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anonymous
  • anonymous
oh sorry
anonymous
  • anonymous
cosx = sqrt(1-4/9)= sqrt(5)/3
anonymous
  • anonymous
cosy =1/4 siny =- sqrt(1-1/16)=sqrt(15)/4
anonymous
  • anonymous
put the values in formula
anonymous
  • anonymous
ok thanks....another questions is to find sin (x+y) with the same variables... can you help me get started on that one also?
anonymous
  • anonymous
oops, once would have been enough
anonymous
  • anonymous
sin(x+y)= sinxcosy-cosxsiny
anonymous
  • anonymous
values are same
anonymous
  • anonymous
thank you
anonymous
  • anonymous
so for cos (x-y) would it be: (√5/3)(1/4)+(-2/3)(√15/4)=(√5/12)+(-2√15/12)= √5-2√15/12
anonymous
  • anonymous
siny is negative in fourth quadrant sin y =-sqrt(15)/4
anonymous
  • anonymous
ok so it would be √5+2√15/12
anonymous
  • anonymous
for sin (x+y) would it be (-2/3)(1/4)-(√5/3)((√15/4)= -2/12-√75/12=-2-5√3/12 are my negatives and positives right?
anonymous
  • anonymous
u again missed that siny is negative
anonymous
  • anonymous
-2/12+√75/12
anonymous
  • anonymous
for sin (x+y) would it be (-2/3)(1/4)-(√5/3)((√15/4)= -2/12-√75/12=-2-5√3/12 are my negatives and positives right?

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