Question

how do i write this as an expression?

cos(pi/5)cos(pi/7)+sin(pi/5)sin(pi/7)

Answer 1

recall
\[\cos(x)\cos(y)+\sin(x)\sin(y)=\cos(x-y)\]

Answer 2

though it is already an expression
I think you meant to simplify the given expression

Answer 3

it would be easy if you change radians to degree
hahah i like degrees o^_^o

Answer 4

how do i write the expression as either the sine, cosine, or tangent of a single angle

Answer 5

recall
\[\rm cos(x)\cos(y)+\sin(x)\sin(y)=\color{reD}{\cos(x-y)}\]
yes you have to find red part

Answer 6

cos pi /5 = ?
cos pi /7 = ?
pi/ 5 = x
pi /7 ] y

Answer 7

thank you

Answer 8

np :-)
let us know what you got :-)