Related Formula
For a function to be continuous at a boundary point x = x₀$x = x_0$, the left-hand limit, right-hand limit, and exact function value must all match:
x → x₀^- f(x) = x → x₀^+ f(x) = f(x₀)$$\lim_{x \to x_0^-} f(x) = \lim_{x \to x_0^+} f(x) = f(x_0)$$
Core Logic
Let's enforce continuity at the critical boundaries, x = 1$x = 1$ and x = 0$x = 0$:
- Continuity at x = 1$x = 1$:
f(1^-) = f(1) = 1² + c(1) + 2 = 3 + c$$f(1^-) = f(1) = 1^2 + c(1) + 2 = 3 + c$$
f(1^+) = 2(1) + 1 = 3$$f(1^+) = 2(1) + 1 = 3$$
Equating both configurations: 3 + c = 3 c = 0$3 + c = 3 \implies c = 0$.
- Continuity at x = 0$x = 0$:
f(0^+) = f(0) = 0² + 0 + 2 = 2$$f(0^+) = f(0) = 0^2 + 0 + 2 = 2$$
f(0^-) = h → 0 (a - b (2h))/(h²)$$f(0^-) = \lim_{h \to 0} \frac{a - b \cos(2h)}{h^2}$$
Using the Taylor expansion (2h) = 1 - (4h²)/(2!) + (16h⁴)/(4!) - = 1 - 2h² + (2)/(3)h⁴ -$\cos(2h) = 1 - \frac{4h^2}{2!} + \frac{16h^4}{4!} - \dots = 1 - 2h^2 + \frac{2}{3}h^4 - \dots$
h → 0 (a - b(1 - 2h² + (2)/(3)h⁴ - ))/(h²) = h → 0 ((a-b) + 2bh² - (2)/(3)bh⁴ + )/(h²)$$\lim_{h \to 0} \frac{a - b\left(1 - 2h^2 + \frac{2}{3}h^4 - \dots\right)}{h^2} = \lim_{h \to 0} \frac{(a-b) + 2bh^2 - \frac{2}{3}bh^4 + \dots}{h^2}$$
For the limit to exist and remain finite, the constant term must vanish: a - b = 0 a = b$a - b = 0 \implies a = b$.
The value of the limit is then equal to 2b$2b$. To satisfy continuity: 2b = 2 b = 1 a = 1$2b = 2 \implies b = 1 \implies a = 1$.
Step 1: Checking Differentiability at x = 0
Evaluating the Left-Hand Derivative (LHD) at x = 0$x = 0$ using values a=1, b=1$a=1, b=1$:
LHD = h → 0 (f(-h) - f(0))/(-h) = h → 0 ((1 - (2h))/(h²) - 2)/(-h)$$\text{LHD} = \lim_{h \to 0} \frac{f(-h) - f(0)}{-h} = \lim_{h \to 0} \frac{\frac{1 - \cos(2h)}{h^2} - 2}{-h}$$
LHD = h → 0 ((2 - (2)/(3)h² + ) - 2)/(-h) = h → 0 (2)/(3)h = 0$$\text{LHD} = \lim_{h \to 0} \frac{\left(2 - \frac{2}{3}h^2 + \dots\right) - 2}{-h} = \lim_{h \to 0} \frac{2}{3}h = 0$$
Evaluating the Right-Hand Derivative (RHD) at x = 0$x = 0$:
RHD = h → 0 (f(h) - f(0))/(h) = h → 0 ((h² + 2) - 2)/(h) = h → 0 h = 0$$\text{RHD} = \lim_{h \to 0} \frac{f(h) - f(0)}{h} = \lim_{h \to 0} \frac{(h^2 + 2) - 2}{h} = \lim_{h \to 0} h = 0$$
Since LHD = RHD = 0$\text{LHD} = \text{RHD} = 0$, the function is fully differentiable at x = 0$x = 0$.
Step 2: Checking Differentiability at x = 1
Evaluating derivatives at x = 1$x = 1$ with parameter c = 0$c = 0$:
- For 0 ≤ x ≤ 1$0 \le x \le 1$, f(x) = x² + 2 f'(x) = 2x f'(1^-) = 2$f(x) = x^2 + 2 \implies f'(x) = 2x \implies f'(1^-) = 2$.
- For x > 1$x > 1$, f(x) = 2x + 1 f'(x) = 2 f'(1^+) = 2$f(x) = 2x + 1 \implies f'(x) = 2 \implies f'(1^+) = 2$.
Since the left derivative equals the right derivative at x = 1$x = 1$, the function is differentiable at x = 1$x = 1$.
Thus, the function is differentiable everywhere, giving m = 0$m = 0$ points of non-differentiability.
Step 3: Finding the Requested Evaluation Sum
Now substitute the values m=0, a=1, b=1, c=0$m=0, a=1, b=1, c=0$ into the target equation:
m + a + b + c = 0 + 1 + 1 + 0 = 2$$m + a + b + c = 0 + 1 + 1 + 0 = 2$$
Pattern Recognition
Sees: Continuity conditions paired with rational surd trigonometric expansion.
Shortcut: When tracking indeterminate limits like (a-b 2x)/(x²)$\frac{a-b\cos 2x}{x^2}$, matching expansions row by row prevents typical computation errors encountered with standard L'Hopital differentiation loops.
Chapter Mix
Class 12 Mathematics: Limits, Continuity and Differentiability