Question

Can you check my solution?

Question: For 0≤t≤5, find when t(cos t)>0.

My answer: t>cos^-1(0).

Thanks.

Answer 1

http://www.wolframalpha.com/input/?i=xcos%28x%29&lk=4

Answer 2

0<cost<=1 all 0<=t<=5

Answer 3

thus
tcost>0 all 0<t<=5 except t=0

Answer 4

no i don't think so

Answer 5

for \(\frac{\pi}{2}<t<\frac{3\pi}{2}\) we have \(\cos(t)<0\)

Answer 6

yes

Answer 7

and so \(t\cos(t)<0\) on that interval as well

Answer 8

point is that when \(0<t<5\) the solution to \(t\cos(t)>0\) is the same as the solution to \(\cos(t)>0\)

Answer 9

@chanh_chung question asks \(>0\) not \(>1\) i think

Answer 10

yes

Answer 11

@satellite73 would the right answer be 0<t<pi/2 and t>3(pi)/2

Answer 12

I say
tcost>0 all 0<t<=5 except t=0 because t=0 is tcost=0