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@ -1,33 +0,0 @@
To solve for a double or half angle identity:
1. Draw a triangle
2. Choose an identity to use
3. Substitute into formula
# Double Angle Identities
Sine:
$$ \sin(2\theta) = 2\sin\theta\cos\theta $$
Cosine:
$$
\begin{matrix}
\cos(2\theta) = \cos^2\theta - \sin^2\theta\\
= 1 - 2sin^2\theta\\
= 2cos^2\theta - 1\\
\end{matrix}
$$
Tan:
$$ \tan(2\theta) = \dfrac{2\tan\theta}{1-\tan^2\theta}$$
## Half Angle Identities
Whether the output is positive or negative depends on what quadrant the output is in.
Sine:
$$ \sin(\frac{\theta}{2}) = \pm\sqrt{\frac{1-\cos\theta}{2}} $$
Cosine:
$$ \cos(\frac{\theta}{2}) = \pm \sqrt{\frac{1 + \cos\theta}{2}} $$
Tangent:
$$
\begin{matrix}
\tan(\dfrac{\theta}{2}) = \pm\sqrt{\dfrac{1-\cos\theta}{1 + \cos\theta}}\\
= \dfrac{\sin\theta}{1 + \cos\theta}\\
= \dfrac{1 - cos\theta}{\sin\theta}
\end{matrix}
$$

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@ -52,17 +52,7 @@ int arr_size = sizeof(arr) / sizeof(arr[0]);
`&` gives you the address of a variable `&` gives you the address of a variable
`*` gives you the value in memory that an address points to. `*` gives you the value in memory that an address points to.
To update the value a pointer points at, you can dereference on the left hand side of the assignment operator:
```c
// Update the value `p` points at to be 7
*p = 7;
```
Because of how operator precedence works, parentheses should be placed around the dereference operator and the variable
```c
// Increment the value pointed to by `p`
(*p)++;
```
# Formatting specifiers # Formatting specifiers
# Standard library # Standard library
## Formatting specifiers ## Formatting specifiers

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@ -23,12 +23,3 @@ middle = low + (high - low) / 2;
The following expressions are illegal because of mismatched types: The following expressions are illegal because of mismatched types:
- (a) `p == a[0]` - Comparison between `int *` and `int` - (a) `p == a[0]` - Comparison between `int *` and `int`
The rest of the expressions are true. The rest of the expressions are true.
8. Rewrite the following function to use pointer arithmetic...
```c
void store_zeros(int *a, int n) {
for (int i = 0; i < n; i++) {
*(a + i) = 0;
}
}
```