- #1
Rijad Hadzic
- 321
- 20
Homework Statement
So in an AC circuit with inductance, I found
[itex] I = (-ε_{max} cos(ωt)) / ωL [/itex]
I want to rewrite this as a sine function.
Homework Equations
The Attempt at a Solution
I can ignore [itex] ε_{max} / ωL [/itex] and work with -cos(ωt)
I set ωt = θ
I know cos(θ) = sin(θ+pi/2)
so -cosθ = -sin(θ+pi/2)
-sinθ = sin(-θ)
so shouldnt
-sin(θ+pi/2) = sin (-θ-pi/2) ?
but my book rewrote cos(ωt) as sin(ωt - pi/2)
How can you write -θ-pi/2 as θ-pi/2?
My hunch is telling me the step
-cosθ = -sin(θ+pi/2)
-cosθ = sin(-θ-pi/2)
is where I made my mistake but I don't understand why.