trig limit ques (1 Viewer)

[jimmik]

can anybody help me wif this plz?

lim 4sin3x/sin2x
x->0

 

[Calculon]

When you have a limit with sinqx/sinzx and x-->0 it ends up being q/z. The answer to this one is 4*3/2=6

if in doubt substitute in 0.00001, not very methodical but it works.

 

[Rahul]

Originally posted by Calculon
if in doubt substitute in 0.00001, not very methodical but it works.

i like using that "method". used 1000 for infinity.

 

[jimmik]

Originally posted by Calculon
When you have a limit with sinqx/sinzx and x-->0 it ends up being q/z. The answer to this one is 4*3/2=6

in an exam can u jus put that as the answer, or jus state since lim x-> 0 for sinqx/sinzx = q/z? dont u need workin out?

 

[ND]

lim 4sin3x/sin2x
=4*lim (sin3x/3x)*(3x/sin2x)
=4*lim (sin3x/3x)*lim (3x/sin2x)
=4*3/2*lim 2x/sin2x
=4*3/2=6

Originally posted by Calculon
When you have a limit with sinqx/sinzx and x-->0 it ends up being q/z. The answer to this one is 4*3/2=6

if in doubt substitute in 0.00001, not very methodical but it works.

I don't think you'd be allowed to assume that.

 

[KeypadSDM]

Originally posted by ND
I don't think you'd be allowed to assume that.

But it's a VERY good check to see if you're right. Saved my ass in 3 unit.

 

[CM_Tutor]

I agree that these sorts of techniques are useful checks (but not explanations / 'proofs'), but be a bit more careful with using the 'large' values, like 1000, for infinity.

 

[MML]

use L'Hopitals Rule; hehehehehe...go learn it, then u can do those q's in seconds. and out smart ur avg highsko teacher

 

[Li0n]

anyone here know of a text book that has questions for that? i got cambridge year 11 thats about it, every other maths text book has no topic called "fundamental limits" as cambridge calls it i think.