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Gegee: $f(x) = 2 - 3x^2$ Bepaal $f'(x)$ vanuit eerste beginsels - NSC Mathematics - Question 7 - 2018 - Paper 1

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Gegee:---$f(x)-=-2---3x^2$---Bepaal-$f'(x)$-vanuit-eerste-beginsels-NSC Mathematics-Question 7-2018-Paper 1.png

Gegee: $f(x) = 2 - 3x^2$ Bepaal $f'(x)$ vanuit eerste beginsels. Bepaal: 7.2 7.2.1 $D_{f}[4x + 5]^2$ 7.2.2 $\frac{dy}{dx}$ indien $y = \sqrt{x^2 - 8} ... show full transcript

Worked Solution & Example Answer:Gegee: $f(x) = 2 - 3x^2$ Bepaal $f'(x)$ vanuit eerste beginsels - NSC Mathematics - Question 7 - 2018 - Paper 1

Step 1

Bepaal $f'(x)$ vanuit eerste beginsels.

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Answer

To determine the derivative of the function using first principles, we apply the limit definition of the derivative:

f(x)=limh0f(x+h)f(x)hf'(x) = \lim_{h \to 0} \frac{f(x + h) - f(x)}{h}

  1. Substitute f(x+h)f(x+h) and f(x)f(x):

    f(x+h)=23(x+h)2=23(x2+2xh+h2)=23x26xh3h2f(x + h) = 2 - 3(x + h)^2 = 2 - 3(x^2 + 2xh + h^2) = 2 - 3x^2 - 6xh - 3h^2

    Therefore,

    f(x)=limh0(23x26xh3h2)(23x2)hf'(x) = \lim_{h \to 0} \frac{(2 - 3x^2 - 6xh - 3h^2) - (2 - 3x^2)}{h}

    Which simplifies to:

    f(x)=limh06xh3h2hf'(x) = \lim_{h \to 0} \frac{-6xh - 3h^2}{h}

    Cancelling hh gives:

    f(x)=limh0(6x3h)f'(x) = \lim_{h \to 0} (-6x - 3h)

    Finally, taking the limit as hh approaches 0 yields:

    f(x)=6xf'(x) = -6x

Step 2

Bepaal $D_{f}[4x + 5]^2$.

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Answer

To find the derivative of Df[4x+5]2D_{f}[4x + 5]^2, we utilize the chain rule:

  1. First, calculate the derivative of the outer function and the inner function:

    If u=4x+5u = 4x + 5, then Df[u2]=2ududxD_{f}[u^2] = 2u \cdot \frac{du}{dx}.

  2. Deriving, we find:

    Df[4x+5]2=16x2+40x+25D_{f}[4x + 5]^2 = 16x^2 + 40x + 25

    Thus:

    Df[4x+5]2=32x+40D_{f}[4x + 5]^2 = 32x + 40.

Step 3

$\frac{dy}{dx}$ indien $y = \sqrt{x^2 - 8} \frac{x^2}{x^2}$.

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Answer

To find rac{dy}{dx} for the function given:

  1. First, express the function clearly by simplifying:

    If y=x28x2x2y = \sqrt{x^2 - 8} \cdot \frac{x^2}{x^2}, note that rac{x^2}{x^2}=1 for x0x \neq 0.

  2. Thus,

    y=x28y = \sqrt{x^2 - 8}

  3. Using implicit differentiation:

    dydx=12x282x=xx28\frac{dy}{dx} = \frac{1}{2\sqrt{x^2 - 8}} \cdot 2x = \frac{x}{\sqrt{x^2 - 8}}.

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