please help me

help me please 1)if tan 1/2 x = t. find cos x.

2)what is coeficient x^3 y^2 z^5 of expanded form (x + 2y - z)^10.

3)a = (2015)^(1/2015). proof that a^(a^(a^(a^(......))) (with the number of a is 2015) < 2015.

4)Given that x^2014 - 1/(x^2014) = 7. find x^2014 + 1/(x^2014)

5)gveni P(x) = 1-x+x^2-x^3+....+x^2014-x^2015. if P(x) substitute with y and y = x+1, what is the coeficient of y^4 ?

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Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$