Merge branch 'section-12.1-typos' of https://github.com/clark-archer/…

…mooculus into development

public/textbook/integrals.tex

@@ -44,7 +44,7 @@ \section{Definite Integrals Compute Signed Area}
 is a triangle, we can use the formula for the area of the triangle to
 compute
 \[
-\int_0^2 x \d x = \frac{1}{2} 3\cdot 3 = 9/2. 
+\int_0^3 x \d x = \frac{1}{2} 3\cdot 3 = 9/2.
 \]
 \end{solution}
 
@@ -274,7 +274,7 @@ \subsection*{Accumulation Functions}
 
 The key point to take from these examples is that an accumulation function
 \[
-\int_a^x f(t) \d x 
+\int_a^x f(t) \d t
 \]
 is increasing precisely when $f(t)$ is positive and is decreasing
 precisely when $f(t)$ is negative. In short, it seems that $f(x)$ is