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anonymous

  • 4 years ago

if a and b are two angles in Quadrant II such that tan a = -1/2 and tan B = -2/3 find cos(a+b)

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  1. anonymous
    • 4 years ago
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    You can use the mother equation to derive cos(a+b)=cos(a)cos(b)-sin(a)sin(b) |dw:1327888004419:dw| -3/2sin(b) = cos(b) -2sin(a) = cos(a) cos(a+b) = 3sin(a)sin(b)-1/3cos(a)cos(b) take your pick = 3/2cos(a)(2/3cos(b))-1/3cos(a)cos(b) = 2/3cos(a)cos(b)

  2. anonymous
    • 4 years ago
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    Thank you for your help on that, is there anyway you could help me with some more math problems? such as 35. Verify that cos(90+A) =-sin A is an identity?

  3. anonymous
    • 4 years ago
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    just plug and chug cos(90+A)=cos(90)cos(A)-sin(90)sin(A) cos(90)=0, since d/dx sin(x)=cos(x) and sin(90)=1, so you have -1*sin(A) = -sin(A)

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