Question
Suppose that $f(x)$ is continuous on (0,2) and never zero there and $f(1)>0$. What can you say about the sign of $f$ on (0,2)$?$
Step 1
This is because if it were to change its sign, it would have to pass through zero, which is not allowed. Show more…
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Let $f:[0,2] \rightarrow \mathbb{R}$ be given by $$ f(x)=\left\{\begin{array}{ll} x & \text { if } 0 \leq x<1 \\ 3-x & \text { if } 1 \leq x \leq 2 \end{array}\right. $$ Show that $f$ assumes every value between 0 and 2 exactly once on $[0,2]$, but $f$ is not continuous on $[0,2]$.
Let $f:[0,2] \rightarrow \mathbb{R}$ be given by $$ f(x):=\left\{\begin{array}{ll} x & \text { if } 0 \leq x<1 \\ 3-x & \text { if } 1 \leq x \leq 2 \end{array}\right. $$ Show that $f$ assumes every value between 0 and 2 exactly once on $[0,2]$, but $f$ is not continuous on $[0,2]$.
Suppose that $f$ is continuous on the interval $[0,1],$ that $f(0)=2,$ and that $f$ has no zeros in the interval. Prove that $f(x)>0$ for all $x$ in [0,1].
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