document.write( "Question 619835: Suppose sinA = 12/13 with 90º≤A≤180º. Suppose also that sinB = -7/25 with -90º≤B≤0º. Find cos(A - B). \n" ); document.write( "

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Suppose sinA = 12/13 with 90º≤A≤180º. Suppose also that sinB = -7/25 with -90º≤B≤0º. Find cos(A - B).
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\n" ); document.write( "cos addition formula: Cos(A-B)=cosAcosB+sinAsinB
\n" ); document.write( "given sin A=12/13=opposite side/hypotenuse
\n" ); document.write( "adjacent side=√(13^2-12^2)=√(169-144)=√25=5
\n" ); document.write( "cos A=adjacent side/hypotenuse=-5/13 (in quadrant II where cos<0)
\n" ); document.write( "..
\n" ); document.write( "given sin B=-7/25=opposite side/hypotenuse
\n" ); document.write( "adjacent side=√(25^2-7^2)=√(625-49)=√576=24
\n" ); document.write( "cos B=adjacent side/hypotenuse=24/25 (in quadrant IV where cos>0)
\n" ); document.write( "..
\n" ); document.write( "Cos(A-B)=-5/13*24/25+12/13*+7/25=-120/325+84/325=-36/325≈-.1108 \n" ); document.write( "

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