ed84c Posted October 2, 2007 Share Posted October 2, 2007 Hi Guys, Just started teaching myself FP2 from home so I might end up with a lot of these.... anyway im trying to integrate sin5xcos2x dx but am running out of ideas. Ive tried to get everything into 2x's but each time I end up with something wierd. Any ideas? Link to comment Share on other sites More sharing options...
Country Boy Posted October 2, 2007 Share Posted October 2, 2007 Looks to me like you need a trig identity! Do you know sin(x+y)= sin(x)cos(y)+ cos(x)sin(y)? If you replace y with -y that becomes sin(x-y)= sin(x)cos(y)- cos(x)sin(y) because cos(-y)= cos(y) and sin(-y)= -sin(y). Adding those two equations, 2sin(x)cos(y)= sin(x+y)+ sin(x-y) or sin(x)cos(y)= (sin(x+y)+ sin(x-y))/2. Now what does that give you for sin(5x)cos(2x)? Link to comment Share on other sites More sharing options...
ed84c Posted October 3, 2007 Author Share Posted October 3, 2007 Cheers for the help, it worked. Link to comment Share on other sites More sharing options...
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