document.write( "Question 364466: Hi All,
\n" ); document.write( " Having difficulty with this particular problem on a task sheet, any help would be greatly appreciated.
\n" ); document.write( " Given a=i+3j-k and b=2i+j-k, find a.b and the cosine of the angle Theta between the vectors\r
\n" ); document.write( "\n" ); document.write( "b) Given a= 3i+j-2k and b= -6i-2j+4k find a.b and the angle theta between vectors\r
\n" ); document.write( "\n" ); document.write( "Finaly c) For what value of alpha will the vectors a+5i+2j+3k and b=2i+alphaj+alphak be perpendicular?\r
\n" ); document.write( "\n" ); document.write( "Many thanks in advance for any help.\r
\n" ); document.write( "\n" ); document.write( "Mike
\n" ); document.write( "

Algebra.Com's Answer #259882 by Fombitz(32388)\"\" \"About 
You can put this solution on YOUR website!
b) Use the dot product.
\n" ); document.write( "\"a\"=(\"3\",\"1\",\"-2\")
\n" ); document.write( "\"b\"=(\"-6\",\"-2\",\"4\")
\n" ); document.write( "\"a%2Ab\"=\"3%28-6%29%2B1%28-2%29%2B%28-2%29%284%29=-18-2-8=-28\"
\n" ); document.write( "\"a%2Ab=abs%28a%29abs%28b%29cos%28theta%29\"
\n" ); document.write( "\"abs%28a%29=sqrt%283%5E2%2B1%5E2%2B%28-2%29%5E2%29=sqrt%289%2B1%2B4%29=sqrt%2814%29\"
\n" ); document.write( "
\n" ); document.write( "\"-28=sqrt%2814%29%282%2Asqrt%2814%29%29cos%28theta%29\"
\n" ); document.write( "\"cos%28theta%29=-28%2F%282%2A14%29\"
\n" ); document.write( "\"cos%28theta%29=-1\"
\n" ); document.write( "\"highlight%28theta=180%29\"
\n" ); document.write( ".
\n" ); document.write( ".
\n" ); document.write( ".
\n" ); document.write( "c)
\n" ); document.write( "Perpendicular means \"theta=90\".
\n" ); document.write( "\"cos%2890%29=0\"
\n" ); document.write( "So then \"a%2Ab=0\"
\n" ); document.write( "\"a\"=(\"5\",\"2\",\"3\")
\n" ); document.write( "\"b\"=(\"2\",\"alpha\",\"alpha\")
\n" ); document.write( "\"a%2Ab\"=\"5%2A2%2B2%2Aalpha%2B3%2Aalpha=10%2B5%2Aalpha\"
\n" ); document.write( "\"10%2B5%2Aalpha=0\"
\n" ); document.write( "\"5%2Aalpha=-10\"
\n" ); document.write( "\"highlight%28alpha=-2%29\"
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