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4 parts
a

dydx=6x−7\frac{dy}{dx} = 6x - 7

b(i)

dydx=7(x−9)6\frac{dy}{dx} = 7(x-9)^6

b(ii)

dydx=2xsin⁡3x+3x2cos⁡3x\frac{dy}{dx} = 2x \sin 3x + 3x^2 \cos 3x

b(iii)

dydx=2x−1\frac{dy}{dx} = 2x - 1

Step-by-step solution

16 steps

Hapa kuna suluhisho la maswali yako ya calculus:

Part a· 4 steps

Differentiate y=3x2−7xy = 3x^2 - 7x from first principles.

Ili kutofautisha kutoka kanuni za kwanza, tunatumia fomula:

f′(x)=lim⁡h→0f(x+h)−f(x)hf'(x) = \lim_{h \to 0} \frac{f(x+h) - f(x)}{h}

Hapa, f(x)=3x2−7xf(x) = 3x^2 - 7x.

  1. Tafuta f(x+h)f(x+h).

    f(x+h)=3(x+h)2−7(x+h)f(x+h) = 3(x+h)^2 - 7(x+h) f(x+h)=3(x2+2xh+h2)−7x−7hf(x+h) = 3(x^2 + 2xh + h^2) - 7x - 7h f(x+h)=3x2+6xh+3h2−7x−7hf(x+h) = 3x^2 + 6xh + 3h^2 - 7x - 7h
  2. Tafuta f(x+h)−f(x)f(x+h) - f(x).

    f(x+h)−f(x)=(3x2+6xh+3h2−7x−7h)−(3x2−7x)f(x+h) - f(x) = (3x^2 + 6xh + 3h^2 - 7x - 7h) - (3x^2 - 7x) f(x+h)−f(x)=3x2+6xh+3h2−7x−7h−3x2+7xf(x+h) - f(x) = 3x^2 + 6xh + 3h^2 - 7x - 7h - 3x^2 + 7x f(x+h)−f(x)=6xh+3h2−7hf(x+h) - f(x) = 6xh + 3h^2 - 7h
  3. Gawanya kwa hh.

    f(x+h)−f(x)h=6xh+3h2−7hh\frac{f(x+h) - f(x)}{h} = \frac{6xh + 3h^2 - 7h}{h} f(x+h)−f(x)h=6x+3h−7\frac{f(x+h) - f(x)}{h} = 6x + 3h - 7
  4. Chukua kikomo kama h→0h \to 0.

    f′(x)=lim⁡h→0(6x+3h−7)f'(x) = \lim_{h \to 0} (6x + 3h - 7) f′(x)=6x−7f'(x) = 6x - 7

    Jibu la mwisho:

    dydx=6x−7\boxed{\frac{dy}{dx} = 6x - 7}

Part b(i)

dydx=7(x−9)6\frac{dy}{dx} = 7(x-9)^6

y=(x−9)7y = (x-9)^7

Differentiate each of the following functions

Tunatumia sheria ya mnyororo (chain rule).

  1. Acha u=x−9u = x-9.

    Kisha y=u7y = u^7.

  2. Tafuta dydu\frac{dy}{du} na dudx\frac{du}{dx}.

    dydu=7u6\frac{dy}{du} = 7u^6 dudx=1\frac{du}{dx} = 1
  3. Tumia sheria ya mnyororo dydx=dydu⋅dudx\frac{dy}{dx} = \frac{dy}{du} \cdot \frac{du}{dx}.

    dydx=7u6⋅1\frac{dy}{dx} = 7u^6 \cdot 1 dydx=7(x−9)6\frac{dy}{dx} = 7(x-9)^6

    Jibu la mwisho:

    dydx=7(x−9)6\boxed{\frac{dy}{dx} = 7(x-9)^6}

Part b(ii)

dydx=2xsin⁡3x+3x2cos⁡3x\frac{dy}{dx} = 2x \sin 3x + 3x^2 \cos 3x

y=x2sin⁡3xy = x^2 \sin 3x

Tunatumia sheria ya bidhaa (product rule): ddx(uv)=u′v+uv′\frac{d}{dx}(uv) = u'v + uv'.

  1. Acha u=x2u = x^2 na v=sin⁡3xv = \sin 3x.

  2. Tafuta u′u' na v′v'.

    u′=ddx(x2)=2xu' = \frac{d}{dx}(x^2) = 2x v′=ddx(sin⁡3x)=cos⁡3x⋅ddx(3x)=3cos⁡3xv' = \frac{d}{dx}(\sin 3x) = \cos 3x \cdot \frac{d}{dx}(3x) = 3 \cos 3x
  3. Tumia sheria ya bidhaa.

    dydx=(2x)(sin⁡3x)+(x2)(3cos⁡3x)\frac{dy}{dx} = (2x)(\sin 3x) + (x^2)(3 \cos 3x) dydx=2xsin⁡3x+3x2cos⁡3x\frac{dy}{dx} = 2x \sin 3x + 3x^2 \cos 3x

    Jibu la mwisho:

    dydx=2xsin⁡3x+3x2cos⁡3x\boxed{\frac{dy}{dx} = 2x \sin 3x + 3x^2 \cos 3x}

Part b(iii)

dydx=2x−1\frac{dy}{dx} = 2x - 1

y=x3+1x+1y = \frac{x^3+1}{x+1}

Kwanza, rahisiisha usemi kwa kutumia utambulisho wa jumla ya cubes a3+b3=(a+b)(a2−ab+b2)a^3+b^3 = (a+b)(a^2-ab+b^2).

  1. Rahisiisha usemi.

    y=(x+1)(x2−x+1)x+1y = \frac{(x+1)(x^2-x+1)}{x+1}

    Kwa x≠−1x \neq -1, usemi unakuwa:

    y=x2−x+1y = x^2-x+1
  2. Tofautisha usemi uliorahisishwa.

    dydx=ddx(x2−x+1)\frac{dy}{dx} = \frac{d}{dx}(x^2-x+1) dydx=2x−1\frac{dy}{dx} = 2x - 1

    Jibu la mwisho:

    dydx=2x−1\boxed{\frac{dy}{dx} = 2x - 1}

Part c· 4 steps

Locate the stationary points of the function z=x3+y3−3x−6y−1z = x^3 + y^3 - 3x - 6y - 1 and hence determine their nature.

Ili kupata pointi za stationary, tunapata derivatives za sehemu ya kwanza na kuziweka sawa na sifuri.

  1. Tafuta derivatives za sehemu ya kwanza.

    ∂z∂x=3x2−3\frac{\partial z}{\partial x} = 3x^2 - 3 ∂z∂y=3y2−6\frac{\partial z}{\partial y} = 3y^2 - 6
  2. Weka derivatives za sehemu sawa na sifuri na utatue kwa xx na yy.

    3x2−3=0  ⟹  3x2=3  ⟹  x2=1  ⟹  x=±13x^2 - 3 = 0 \implies 3x^2 = 3 \implies x^2 = 1 \implies x = \pm 1 3y2−6=0  ⟹  3y2=6  ⟹  y2=2  ⟹  y=±23y^2 - 6 = 0 \implies 3y^2 = 6 \implies y^2 = 2 \implies y = \pm \sqrt{2}

    Pointi za stationary ni: (1,2)(1, \sqrt{2}), (1,−2)(1, -\sqrt{2}), (−1,2)(-1, \sqrt{2}), (−1,−2)(-1, -\sqrt{2}).

  3. Tafuta derivatives za sehemu ya pili ili kuamua asili ya pointi.

    ∂2z∂x2=6x\frac{\partial^2 z}{\partial x^2} = 6x ∂2z∂y2=6y\frac{\partial^2 z}{\partial y^2} = 6y ∂2z∂x∂y=0\frac{\partial^2 z}{\partial x \partial y} = 0

    Tunatumia mtihani wa derivative ya pili na discriminant D=∂2z∂x2∂2z∂y2−(∂2z∂x∂y)2D = \frac{\partial^2 z}{\partial x^2} \frac{\partial^2 z}{\partial y^2} - \left(\frac{\partial^2 z}{\partial x \partial y}\right)^2.

  4. Tathmini kila pointi ya stationary.

    • Kwa pointi (1,2)(1, \sqrt{2}):
    ∂2z∂x2=6(1)=6\frac{\partial^2 z}{\partial x^2} = 6(1) = 6 ∂2z∂y2=62\frac{\partial^2 z}{\partial y^2} = 6\sqrt{2} D=(6)(62)−(0)2=362D = (6)(6\sqrt{2}) - (0)^2 = 36\sqrt{2}

    Kwa kuwa D>0D > 0 na ∂2z∂x2>0\frac{\partial^2 z}{\partial x^2} > 0, pointi hii ni local minimum.

    • Kwa pointi (1,−2)(1, -\sqrt{2}):
    ∂2z∂x2=6(1)=6\frac{\partial^2 z}{\partial x^2} = 6(1) = 6 ∂2z∂y2=6(−2)=−62\frac{\partial^2 z}{\partial y^2} = 6(-\sqrt{2}) = -6\sqrt{2} D=(6)(−62)−(0)2=−362D = (6)(-6\sqrt{2}) - (0)^2 = -36\sqrt{2}

    Kwa kuwa D<0D < 0, pointi hii ni saddle point.

    • Kwa pointi (−1,2)(-1, \sqrt{2}):
    ∂2z∂x2=6(−1)=−6\frac{\partial^2 z}{\partial x^2} = 6(-1) = -6 ∂2z∂y2=62\frac{\partial^2 z}{\partial y^2} = 6\sqrt{2} D=(−6)(62)−(0)2=−362D = (-6)(6\sqrt{2}) - (0)^2 = -36\sqrt{2}

    Kwa kuwa D<0D < 0, pointi hii ni saddle point.

    • Kwa pointi (−1,−2)(-1, -\sqrt{2}):
    ∂2z∂x2=6(−1)=−6\frac{\partial^2 z}{\partial x^2} = 6(-1) = -6 ∂2z∂y2=6(−2)=−62\frac{\partial^2 z}{\partial y^2} = 6(-\sqrt{2}) = -6\sqrt{2} D=(−6)(−62)−(0)2=362D = (-6)(-6\sqrt{2}) - (0)^2 = 36\sqrt{2}

    Kwa kuwa D>0D > 0 na ∂2z∂x2<0\frac{\partial^2 z}{\partial x^2} < 0, pointi hii ni local maximum.

    Jibu la mwisho:
    Pointi za stationary na asili yake ni:

    • (1,2)(1, \sqrt{2}): local minimum
    • (1,−2)(1, -\sqrt{2}): saddle point
    • (−1,2)(-1, \sqrt{2}): saddle point
    • (−1,−2)(-1, -\sqrt{2}): local maximum
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