\( \sum _ { n = 1 } ^ { \infty } ( - 1 ) ^ { n - 1 } \frac { 7 ^ { n } } { 5 ^ { n } n ^ { 3 } } \)

Show that \( F(x)=|x| \) is continuous everywhere.

11. Find the values of \( a \) and \( b \) that make \( f \) continuous everywhere. \[ f(x)=\left\{\begin{array}{ll}\frac{x^{2}-4}{x-2} & \text { if } x<2 \\ a x^{2}-b x+3 & \text { if } 2 \leq x<3 \\ 2 x-a+b & \text { if } x \geq 3\end{array}\right. \]

Suppose \( f \) is continuous on \( [1,5] \) and the only solutions of the equation \( f(x)= \) 6 are \( x=1 \) and \( x=4 \). If \( f(2)=8 \), explain why \( f(3)>6 \). Show that \( F(x)=|x| \) is continuous evervwhere.

8. If \( f(x)=x^{2}+10 \sin x \), show that there is a number \( c \) such that \( f(x)=1000 \).

USing first principle prove that \( y=\sin x \) then \( \frac{d y}{d x}=\cos x \)