# help with this (solving trig eqn, proving identity, etc)

#### isuckatmath

##### New member
1) How would you solve:

cosx=secx

2) prove this is true
sin2x+sin4x -tan3x=0
cos2x+cos4x

last one..

3) if R=v^2sin2x/g
and v=40 R110
solve for x

#### stapel

##### Super Moderator
Staff member
1) A good first step would be to convert everything to sines and cosines. What can you then do with the equation?

2) Your formatting is ambiguous. Do you mean the following?

. . . . .$$\displaystyle \large{\frac{\sin{(2x)}\,+\,\sin{(4x)}} {\cos{(2x)}\,+\,\cos{(4x)}}\, -\,\tan{(3x)}\, =\,0}$$

If so, what identities have you applied? How far have you gotten?

. . . . .$$\displaystyle \large{R\, =\,\frac{v^2\,\sin{(2x)}}{g}}$$