# Tan²(π/5)-1/sin²(3π/10) = ? Simple Trig question?

• Feb 4th 2010, 04:16 PM
Voluntarius Disco
Tan²(π/5)-1/sin²(3π/10) = ? Simple Trig question?
Work:
sin²(π/5)/cos²(π/5)-1/sin²(3π/10)
=sin²36/cos²36-1/sin²54
1/sin²54=1/cos²36
=sin²36-1/cos²36
Yea or nay? [:
• Feb 5th 2010, 11:36 AM
Henryt999
What of this....
Quote:

Originally Posted by Voluntarius Disco
Work:
sin²(π/5)/cos²(π/5)-1/sin²(3π/10)
=sin²36/cos²36-1/sin²54
1/sin²54=1/cos²36
=sin²36-1/cos²36
Yea or nay? [:

What of this is given and what have you calculated?
• Feb 5th 2010, 12:02 PM
Voluntarius Disco
Tan²(π/5)-1/sin²(3π/10)is the problem I was given
Under work should be the problem restated and then my inferences/work. Sorry if that was confusing!
• Feb 5th 2010, 12:45 PM
Henryt999
Well
Quote:

Originally Posted by Voluntarius Disco
Work:
sin²(π/5)/cos²(π/5)-1/sin²(3π/10)
=sin²36/cos²36-1/sin²54
1/sin²54=1/cos²36
=sin²36-1/cos²36
Yea or nay? [:

I´m sorry one more question.
You have an expression $tan^2(n/5)-\frac{1}{sin^2(\frac{3n}{10})}$
That expression does not equal anyting (at least not anything we know).
So I supposed you are to break out n.

But you substitute $(n/5)$ for 36.
So that is only valid if n = 180?
But also the expression gains one = sign meaning it is now an equation. From the second row you have these, what is the operator between them?
=sin²36/cos²36-1/sin²54
$(+-\times)$?
1/sin²54=1/cos²36
Im sorry I have no idea if what you have done is correct. If it is an equation and not an expression you can just pop you final values into the equation and se if it is correct.
Remember if you have an expression like x^2+3x+4 you cant´automatically assume that that equals zero and then solve for x.
Post exactly what you want me to check...
• Feb 6th 2010, 02:11 AM
HallsofIvy
I would assume that the problem, which could be done approximately just by using a calculator, asks for an exact value. You haven't found any value or solved the problem, you've just changed from radians to degrees.