Question

What's wrong with this?
4 = 4 [tan(π/4)]
= 4sin(π/4) / cos(π/4)
= 2 sin(π/2) / cos^2 (π/4)
= sin(π) / [cos^2 (π/4) cos(π/2)]
= 0/ 0?!

Answer 1

cos(pi/2) is zero, so you multiplied something by 0/0. =))

Answer 2

But the point is how to correct it?

Answer 3

For this step : sin(π) / [cos^2 (π/4) cos(π/2)]
we should not multiply 0/0
4sin(π/4) / cos(π/4)
=2sin(π/2)/cos^2 (π/4)
=2sin(π/2)/ (1/2)(cos(π/2) +1)
=4sin(π/2)
=4

Answer 4

I see.... So the double angle formula has its 'limitation' ... I'll not make the same mistake again! Thank you :)

Answer 5

4 = 4 tan(π/4)
1 = tan (π/4)
tan (π/4) = tan(π/4)

Answer 6

That's why I chose tan(π/4) :P

Answer 7

it should be limitation of fraction :D

Answer 8

lol My math is not good. Sorry... limitation of fraction!~

Answer 9

Oops, it's so obvious! tan (π/4) = 1

Answer 10

Hey, think simple, will you!
1 = tan(π/4)
= sin(π/4)/ cos(π/4)
= 1
always true :P

Answer 11

I know~ But I was getting 4 = 0/0 :S
Now, I know what's wrong :)