SOLUTION: i have a question that appears on your site, however as i progressed with my answer i have come to a difficult point and am stuck. this is what i have got so far; E=Fs =7sin(t

Question 24976: i have a question that appears on your site, however as i progressed with my answer i have come to a difficult point and am stuck. this is what i have got so far;
E=Fs
=7sin(t-60)*4sin(t+30) which can use the idenitity-
2sinAsinB=cos(A+B)-cos(A+B)
=0.5(cos((t-60)-(t+30))-cos((t-60)+(t+30)))
=0.5(cos(t-60-t-30)-cos(t-60+t+30))
=0.5(cos(-90)-cos(2t-30))
=0.5*0-cos(2t-30)
And thats where i got up to, i know the answer should some how get to;
-14cos(2t-30)
But i just cannot get there, can you tell me where i am going wrong and point me there please.
this is the question; the displacement of a body is given by s=4sin(t+30), and a force acting upon the body is given by F=7sin(t-60). If the energy of the motion, E, at time t is the product Fs, show that E=-14cos(2t-30)
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Somewhere along the line you forgot the "7" and the "4"
that are part of your problem. Multiply your answer by
7*4 and you will have the answer you are looking for.
Cheers,
Stan H.
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