# Homework Help: Linearising cosine

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1. Oct 14, 2015

### Agrajag

1. The problem statement, all variables and given/known data
Linearise the following equation I(theta) = (I1 – I2 ) cos (2theta) + I2
where I1 and I2 are constants.

2. Relevant equations
I(theta) = (I1 – I2 ) cos (2theta) + I2

3. The attempt at a solution
Not sure how to linearise the cos(2theta). Have tried trig identities, would the best option be to take roots of both sides of the equation?

2. Oct 14, 2015

### friendbobbiny

Hi Agrajag, what do you mean by linearize? I usually understand "linearization" to mean: find the closest linear approximation to the given curve. This can be found by taking the derivative at a point to be the slope of a line that goes through that same point. This line is your linearization.

3. Oct 14, 2015

### Agrajag

Hi friendbobbiny, the final equation should be in the form y=mx+c where y is I(theta) and x is theta.

4. Oct 14, 2015

### friendbobbiny

In that case, my approach works! Have you read into finding a linearization by taking a derivative at some point of interest (or at any point of interest)?