Limits problem

1. chukie

80
Solve:
lim x->0 (tan 3(x+h)-tan(3x))/h

i hv no clue where to start =(

2. rootX

err.. tan (3h)/h?

simply plugging in 0 for x..

edit: are you sure x is approaching 0?

initially, I thought it's h..

then the answer would have been 3+3tan(3x)^2
and you had to do some mess with identites..
http://www.clarku.edu/~djoyce/trig/identities.html

Last edited: Jun 9, 2008
3. Dick

25,893
Did you mean lim h->0??

4. chukie

80
sry, yes i mean lim h->0

5. Dick

25,893
Look up a formula for tan(A+B) and apply it to tan(3x+3h). Then simplify, take your limit and use some trig.

6. rootX

It is actually very simple.. don't even need to any trig after simplifying tan(3x+3h) ..

should factor out things.. and they would cancel out nicely.

And, one more thing tan(x)/x = 1 .. (which is simple to prove is you know sin(x)/x =1 as x-->0)

7. Dick

25,893
Yep. You don't have to use any trig. But using sec^2(A)=1+tan^2(A) would put it in the simpler form listed in books.

8. chukie

80
kk thanks i got it =)