Math Is Fun Forum

Stuck on this one maybe stuck on stupid too.   I just can't get it to work out correctly

Here it is :

complete the identity : sec^4x +sec^2x tan^2x-2tan^4x=?

I can not come up with any of the below

4sec^2x
3sec^2x-2
sec^2x+2
tan^2x-1
Hellpppppppp!

My book really isn't clear on how to do this one:

Find another repersentation, (r, θ ), for the point under the given conditions.
                                            (4,pi/4)r>0 and-2pi<θ <0

Clueless........................

Ok this one is use Heron's formula to find the area of the triangle.  It sounded like it was going to be complicated by the name but when I looked at how to work it out it seemed easy. 

here is the problem:  a=13 meters, b=19 meters, c = 10 meters So.......

to begin the Heron's formula I did this

s=1/2(a+b+c) = 1/2(13+19+10)=42 then

AREA= sqrt 42(42-13)(42-19)(42-10)
        = sqrt 896448

I think but, this is where I get lost.

Ok Ok... I have to try this one again.  I have looked every where and re-read the paragraph on the powers of trig functions, nothing was revealing (to me any way).   Here's my repost to my orginal.

Help me guys  there is got to be some soultion on how to work this out. 

Mathsyperson:  thanks for the laugh I agree the book shows examples of the Trig functions with powers .  Then ask to figure out  cos 4x however it does proved multiple choice answers of:
3-4 cos 2x + 4x / 8
or
2-4 cos 2x + 4x /8
or
3-2 cos 2x + 4x /8
or
3+4 cos 2x + 4x /8

I tired a little backwards thinking but still can't figure it out and more feed back you can add is welcome and I checked again,  unless its a typo  it does say  "cos 4x"

Ok here we go again
I have to answer the following:

Rewrite the expression as an equivalent expression that does not contain powers of trigonometirc funcitons greater than 1.

a) cos 4x     b) cos 3x

They dont look like they have powers to me.  Guess I am real dumb when it come to these type of questions