Limits, Continuity & Differentiability
General
Grade 12
Question:
<p>Given <span class="math-inline">\(f\)</span> piecewise defined. <span class="math-inline">\(f_1(x)=|f(|x|)|\)</span>. If <span class="math-inline">\(f\)</span> is continuous in <span class="math-inline">\([-2,10]\)</span>, then:</p>
Step-by-Step Solution
Key Concept: General
Step 1: Determine $k$ using continuity at $x=4$.
For $f(x)$ to be continuous at $x=4$, the left-hand limit must equal the right-hand limit.
$$ \lim_{x \to 4^-} f(x) = \lim_{x \to 4^+} f(x) $$
$$ (4)^2 - 5(4) + 6 = k - \tan\left(\frac{\pi(4)}{4}\right) $$
$$ 16 - 20 + 6 = k - \tan(\pi) $$
$$ 2 = k - 0 $$
$$ k = 2 $$
Step 2: Determine $\alpha$ using continuity at $x=5$.
For $f(x)$ to be continuous at $x=5$, the left-hand limit must equal the right-hand limit.
$$ \lim_{x \to 5^-} f(x) = \lim_{x \to 5^+} f(x) $$
Substitute $k=2$ into the expression for $f(5^-)$:
$$ k - \tan\left(\frac{\pi(5)}{4}\right) = \log_{10}(\alpha(5)) $$
$$ 2 - \tan\left(\frac{5\pi}{4}\right) = \log_{10}(5\alpha) $$
Since $\tan\left(\frac{5\pi}{4}\right) = \tan\left(\pi + \frac{\pi}{4}\right) = \tan\left(\frac{\pi}{4}\right) = 1$:
$$ 2 - 1 = \log_{10}(5\alpha) $$
$$ 1 = \log_{10}(5\alpha) $$
Convert the logarithmic equation to an exponential equation:
$$ 5\alpha = 10^1 $$
$$ 5\alpha = 10 $$
$$ \alpha = 2 $$
Correct Answer: A,C