Related Formula
For a limit of the form x → 0 [g(x)]h(x)$\lim_{x \to 0} [g(x)]^{h(x)}$ where g(x) → 1$g(x) \to 1$ and h(x) → ∞$h(x) \to \infty$, the limit evaluates to:
e^ x → 0 h(x)[g(x) - 1]$$e^{\lim_{x \to 0} h(x)[g(x) - 1]}$$
Core Logic
Given the limit expression:
x → 0 (f(2 + x))3/x = eα$$\lim_{x \to 0} (f(2 + x))^{3/x} = e^{\alpha}$$
Using the standard form as f(2)=1$f(2)=1$, this transforms to:
e^ x → 0 (3)/(x) (f(2 + x) - 1) = eα$$e^{\lim_{x \to 0} \frac{3}{x} (f(2 + x) - 1)} = e^{\alpha}$$
Recognizing the definition of the derivative f'(2) = x → 0 (f(2+x)-1)/(x)$f'(2) = \lim_{x \to 0} \frac{f(2+x)-1}{x}$:
e3 f'(2) = eα$$e^{3 f'(2)} = e^{\alpha}$$
Given f'(2) = 4$f'(2) = 4$:
e3(4) = e¹² = eα α = 12$$e^{3(4)} = e^{12} = e^{\alpha} \implies \alpha = 12$$
Step 1: Finding Intersection points with x-axis
Substitute α = 12$\alpha = 12$ into the equation of the curve:
y = 4x³ - 4x² - 4(12 - 7)x - 12$$y = 4x^3 - 4x^2 - 4(12 - 7)x - 12$$
y = 4x³ - 4x² - 20x - 12$$y = 4x^3 - 4x^2 - 20x - 12$$
To find where it meets the x-axis, set y = 0$y = 0$:
4x³ - 4x² - 20x - 12 = 0 x³ - x² - 5x - 3 = 0$$4x^3 - 4x^2 - 20x - 12 = 0 \implies x^3 - x^2 - 5x - 3 = 0$$
Testing for rational roots, x = -1$x = -1$ is a root because (-1)³ - (-1)² - 5(-1) - 3 = -1 - 1 + 5 - 3 = 0$(-1)^3 - (-1)^2 - 5(-1) - 3 = -1 - 1 + 5 - 3 = 0$.
Step 2: Factoring the cubic polynomial
Dividing x³ - x² - 5x - 3$x^3 - x^2 - 5x - 3$ by (x+1)$(x+1)$ gives:
(x + 1)(x² - 2x - 3) = 0$$(x + 1)(x^2 - 2x - 3) = 0$$
(x + 1)(x + 1)(x - 3) = 0 (x + 1)²(x - 3) = 0$$(x + 1)(x + 1)(x - 3) = 0 \implies (x + 1)^2(x - 3) = 0$$
The roots are x = -1$x = -1$ (repeated root) and x = 3$x = 3$. Therefore, the distinct real values of x$x$ where the curve intersects the x-axis are -1$-1$ and 3$3$, meaning it meets the x-axis exactly 2$2$ times.
Pattern Recognition
A repeated root like (x+1)²$(x+1)^2$ means the curve is tangent to the x-axis at that point, but it still counts as a meeting point. Always count distinct real roots when determining the number of meeting points with the coordinate axes.
Chapter Mix
Class 12 Mathematics: Limits, Continuity and Differentiability
Class 11 Mathematics: Theory of Equations