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>
α=2
α=4
k=2
k=4

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

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