Question

Prove tan5utan3u=(tan^24utan^2u)/(1-tan^24utan^2u)

Answer 1

`\tan5u\tan3u=(\tan^24u\tan^2u)/(1-\tan^24u\tan^2u)`

This is not true (assuming I've understood the question correctly).

Consider
`u=\frac\pi4`. Then


`\tan\frac{5\pi}4\tan\frac{3\pi}4=1(-1)=-1`

while


`(\tan^2\pi\tan^2\frac\pi4)/(1-\tan^2\pi\tan^2\frac\pi4)=(0(1))/(1-0(1))=0`