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education/math/MATH1060 (trig)/Double and Half Angle Identities.md

@@ -0,0 +1,33 @@
+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:
+$$
+\begin{matrix}
+\tan(\dfrac{\theta}{2}) = \pm\sqrt{\dfrac{1-\cos\theta}{1 + \cos\theta}}\\
+= \dfrac{\sin\theta}{1 + \cos\theta}\\
+= \dfrac{1 - cos\theta}{\sin\theta}
+\end{matrix}
+$$

education/software development/ECE1400/C.md

@@ -52,7 +52,17 @@ int arr_size = sizeof(arr) / sizeof(arr[0]);
 `&` gives you the address of a variable
 `*` 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
 # Standard library
 ## Formatting specifiers

education/software development/ECE1400/Chapter 12 Exercises.md

@@ -23,3 +23,12 @@ middle = low + (high - low) / 2;
 The following expressions are illegal because of mismatched types:
 - (a) `p == a[0]` - Comparison between `int *` and `int`
 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;
+    }
+}
+```