# Difficult trig proof

#### Scrutinize

##### Junior Member
Attached is the question with all the work I did and where I got stuck. Any help would be very much appreciated, thanks!

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#### Scrutinize

##### Junior Member
EDIT:

Its a solve for x not a proof, I read the question wrong. Oops

#### Jomo

##### Elite Member
3/2 is NOT 2 + 1/2

#### Scrutinize

##### Junior Member
Yea I realized that when I went back and saw it was an equation not a proof. Dumb mistake on my part

#### Jomo

##### Elite Member
So can we see your updated work.

#### Scrutinize

##### Junior Member
My updated work is completely wrong as well and it would only confuse you guys because it’s like 3 pages long. Basically I’m finding it hard to figure out the easiest way to approach it.

#### pka

##### Elite Member
My updated work is completely wrong as well and it would only confuse you guys because it’s like 3 pages long. Basically I’m finding it hard to figure out the easiest way to approach it.
Look at this graph. Are you sure about problem?

#### Scrutinize

##### Junior Member
Look at this graph. Are you sure about problem?
On my test I'd have to solve it algebraically and show a lot of work. And I can't find the right way to approach it by solving algebraically.

#### pka

##### Elite Member
On my test I'd have to solve it algebraically and show a lot of work. And I can't find the right way to approach it by solving algebraically.
The point is: the graph shows that the equality is not true.
It cannot proven if it is not true.

#### Dr.Peterson

##### Elite Member
You are trying to solve (not prove) $$\displaystyle \cos(2x)=\cos^2\left(\frac{3x}{2}\right)$$.

I would start with a substitution, u = x/2, and then expand using identities for cos(4u) and cos(3u). Then solve for cos(u).

#### MarkFL

##### Super Moderator
Staff member
You posted this same question before:

#### pka

##### Elite Member
You are trying to solve (not prove) $$\displaystyle \cos(2x)=\cos^2\left(\frac{3x}{2}\right)$$.
That was not what was in the OP. Look at this SOLUTION.

#### pka

##### Elite Member
Look at post #2
Right! But this is a perfect example why there should be some way to correct a post that is carried through the entire thread.
In all fairness, you must admit that posts after #2 still assumed 'prove' and not 'solve'.

#### Scrutinize

##### Junior Member
Yea sorry I miss typed the original post and corrected it in a second post but i guess most of you didn't see it, that's my bad. It didn't let me edit what I wrote so I just posted again saying that. Either way like @MarkFL said, I did post this question previously and I was helped with it. I forgot how to do it I guess and forgot i posted about it. (I've been doing tons of different types of math questions these past few weeks and I guess I got lost). My mistake sorry for that.