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Differentiate the following equations: a) y = (ln x)/x2 b) y = (x3 + 3x)5 c) y = e^(2x) sin x d) y = 2x4 − 5x2 + 6x + 1

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5 parts
a

1−2ln⁡xx3\frac{1 - 2 \ln x}{x^3}

b

15(x3+3x)4(x2+1)15(x^3 + 3x)^4 (x^2 + 1)

c

e2x(2sin⁡x+cos⁡x)e^{2x}(2 \sin x + \cos x)

d

8x3−10x+68x^3 - 10x + 6

2
3, 5, 7, 9
6, 22, 46, 78

4n2+4n−24n^2 + 4n - 2

Step-by-step solution

13 steps

Let's solve Question 1 and Question 2.

Part 1

Differentiate the following equations

Part a

1−2ln⁡xx3\frac{1 - 2 \ln x}{x^3}

y=ln⁡xx2y = \frac{\ln x}{x^2}

  1. Apply the quotient rule ddx(uv)=u′v−uv′v2\frac{d}{dx}\left(\frac{u}{v}\right) = \frac{u'v - uv'}{v^2}.

    Let u=ln⁡x  ⟹  u′=1xu = \ln x \implies u' = \frac{1}{x}.
    Let v=x2  ⟹  v′=2xv = x^2 \implies v' = 2x.

    dydx=(1x)(x2)−(ln⁡x)(2x)(x2)2\frac{dy}{dx} = \frac{\left(\frac{1}{x}\right)(x^2) - (\ln x)(2x)}{(x^2)^2}
  2. Simplify the expression.

    dydx=x−2xln⁡xx4\frac{dy}{dx} = \frac{x - 2x \ln x}{x^4} dydx=x(1−2ln⁡x)x4\frac{dy}{dx} = \frac{x(1 - 2 \ln x)}{x^4} dydx=1−2ln⁡xx3\frac{dy}{dx} = \boxed{\frac{1 - 2 \ln x}{x^3}}

Part b

15(x3+3x)4(x2+1)15(x^3 + 3x)^4 (x^2 + 1)

y=(x3+3x)5y = (x^3 + 3x)^5

  1. Apply the chain rule ddx(f(g(x)))=f′(g(x))g′(x)\frac{d}{dx}(f(g(x))) = f'(g(x))g'(x).

    Let g(x)=x3+3xg(x) = x^3 + 3x, so g′(x)=3x2+3g'(x) = 3x^2 + 3.
    Let f(u)=u5f(u) = u^5, so f′(u)=5u4f'(u) = 5u^4.

    dydx=5(x3+3x)4⋅(3x2+3)\frac{dy}{dx} = 5(x^3 + 3x)^4 \cdot (3x^2 + 3)
  2. Factor out common terms.

    dydx=5(x3+3x)4⋅3(x2+1)\frac{dy}{dx} = 5(x^3 + 3x)^4 \cdot 3(x^2 + 1) dydx=15(x3+3x)4(x2+1)\frac{dy}{dx} = \boxed{15(x^3 + 3x)^4 (x^2 + 1)}

Part c

e2x(2sin⁡x+cos⁡x)e^{2x}(2 \sin x + \cos x)

y=e2xsin⁡xy = e^{2x} \sin x

  1. Apply the product rule ddx(uv)=u′v+uv′\frac{d}{dx}(uv) = u'v + uv'.

    Let u=e2x  ⟹  u′=2e2xu = e^{2x} \implies u' = 2e^{2x}.
    Let v=sin⁡x  ⟹  v′=cos⁡xv = \sin x \implies v' = \cos x.

    dydx=(2e2x)(sin⁡x)+(e2x)(cos⁡x)\frac{dy}{dx} = (2e^{2x})(\sin x) + (e^{2x})(\cos x)
  2. Factor out the common term e2xe^{2x}.

    dydx=e2x(2sin⁡x+cos⁡x)\frac{dy}{dx} = \boxed{e^{2x}(2 \sin x + \cos x)}

Part d

8x3−10x+68x^3 - 10x + 6

y=2x4−5x2+6x+1y = 2x^4 - 5x^2 + 6x + 1

  1. Differentiate each term using the power rule.

    dydx=ddx(2x4)−ddx(5x2)+ddx(6x)+ddx(1)\frac{dy}{dx} = \frac{d}{dx}(2x^4) - \frac{d}{dx}(5x^2) + \frac{d}{dx}(6x) + \frac{d}{dx}(1) dydx=2(4x3)−5(2x1)+6(1)+0\frac{dy}{dx} = 2(4x^{3}) - 5(2x^{1}) + 6(1) + 0 dydx=8x3−10x+6\frac{dy}{dx} = \boxed{8x^3 - 10x + 6}

Part 23, 5, 7, 9

Two sequences Un=2n+1U_n = 2n+1 and Vn=Un2−3V_n = U_n^2 - 3 for n≥1n \ge 1.

I. Write down the first four terms of the sequence (UnU_n).

  1. Substitute n=1,2,3,4n=1, 2, 3, 4 into Un=2n+1U_n = 2n+1.

    For n=1:U1=2(1)+1=3n=1: U_1 = 2(1) + 1 = 3
    For n=2:U2=2(2)+1=5n=2: U_2 = 2(2) + 1 = 5
    For n=3:U3=2(3)+1=7n=3: U_3 = 2(3) + 1 = 7
    For n=4:U4=2(4)+1=9n=4: U_4 = 2(4) + 1 = 9
    The first four terms are 3,5,7,9\boxed{3, 5, 7, 9}.

    II. Hence, write down the first four terms of the sequence (VnV_n).

  2. Substitute the terms of UnU_n into Vn=Un2−3V_n = U_n^2 - 3.

    For n=1:V1=U12−3=32−3=9−3=6n=1: V_1 = U_1^2 - 3 = 3^2 - 3 = 9 - 3 = 6
    For n=2:V2=U22−3=52−3=25−3=22n=2: V_2 = U_2^2 - 3 = 5^2 - 3 = 25 - 3 = 22
    For n=3:V3=U32−3=72−3=49−3=46n=3: V_3 = U_3^2 - 3 = 7^2 - 3 = 49 - 3 = 46
    For n=4:V4=U42−3=92−3=81−3=78n=4: V_4 = U_4^2 - 3 = 9^2 - 3 = 81 - 3 = 78
    The first four terms are 6,22,46,78\boxed{6, 22, 46, 78}.

    III. Show that Vn=4n2+4n−2V_n = 4n^2 + 4n - 2.

  3. Substitute Un=2n+1U_n = 2n+1 into the expression for VnV_n.

    Vn=(2n+1)2−3V_n = (2n+1)^2 - 3
  4. Expand the squared term and simplify.

    Vn=(4n2+4n+1)−3V_n = (4n^2 + 4n + 1) - 3 Vn=4n2+4n−2V_n = \boxed{4n^2 + 4n - 2}

    IV. Determine whether the sequence UnU_n and VnV_n is a GP or AP.

  5. Check UnU_n for AP and GP.

    The terms of UnU_n are 3,5,7,9,…3, 5, 7, 9, \dots
    Common difference: U2−U1=5−3=2U_2 - U_1 = 5 - 3 = 2. U3−U2=7−5=2U_3 - U_2 = 7 - 5 = 2.
    Since there is a constant common difference, UnU_n is an Arithmetic Progression (AP).
    Common ratio: U2U1=53\frac{U_2}{U_1} = \frac{5}{3}. U3U2=75\frac{U_3}{U_2} = \frac{7}{5}. Since the ratios are not equal, UnU_n is not a GP.

  6. Check VnV_n for AP and GP.

    The terms of VnV_n are 6,22,46,78,…6, 22, 46, 78, \dots
    Common difference: V2−V1=22−6=16V_2 - V_1 = 22 - 6 = 16. $V_3

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