Question

what does it mean
cos7(root over 5)x
i mean how it should be written

Answer 1

you mean
\[\cos(\sqrt[7]{5}x)\]?
then\[=\cos\left(5^{1\over7}x\right)\]

Answer 2

okay

Answer 3

were you asking how to write that in TeX?

Answer 4

yes

Answer 5

\sqrt[n]{x}
produces
\[\sqrt[n]{x}\]