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Evaluate all the following: i) Lim 2x+3 / 4x+3 ii) Lim x->0 x/(x2+2) iii) y=(3x3−8x2−1)6 iv) 4xy+y2 = x2+2

Mathematics

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Question 1: Evaluate all the following

i) lim⁡x→∞2x+38x+1\lim_{x \to \infty} \frac{2x+3}{8x+1}

  1. Divide the numerator and denominator by the highest power of xx, which is xx.

    lim⁡x→∞2xx+3x8xx+1x=lim⁡x→∞2+3x8+1x\lim_{x \to \infty} \frac{\frac{2x}{x}+\frac{3}{x}}{\frac{8x}{x}+\frac{1}{x}} = \lim_{x \to \infty} \frac{2+\frac{3}{x}}{8+\frac{1}{x}}
  2. Apply the limit.

    As x→∞x \to \infty, 3x→0\frac{3}{x} \to 0 and 1x→0\frac{1}{x} \to 0.

    2+08+0=28\frac{2+0}{8+0} = \frac{2}{8}
  3. Simplify the fraction.

    28=14\frac{2}{8} = \frac{1}{4}

    The limit is 14\boxed{\frac{1}{4}}.

    ii) lim⁡x→02x2+8x+3x2+2\lim_{x \to 0} \frac{2x^2+8x+3}{x^2+2}

  4. Substitute x=0x=0 into the expression, as the denominator is not zero at x=0x=0.

    2(0)2+8(0)+3(0)2+2\frac{2(0)^2+8(0)+3}{(0)^2+2}
  5. Simplify the expression.

    0+0+30+2=32\frac{0+0+3}{0+2} = \frac{3}{2}

    The limit is 32\boxed{\frac{3}{2}}.

    Question 2: Find dydx\frac{dy}{dx} of the following

    i) y=3x2−84x+3y = \frac{3x^2-8}{4x+3}

  6. Apply the quotient rule, dydx=u′v−uv′v2\frac{dy}{dx} = \frac{u'v - uv'}{v^2}, where u=3x2−8u = 3x^2-8 and v=4x+3v = 4x+3.

    Then u′=6xu' = 6x and v′=4v' = 4.

    dydx=(6x)(4x+3)−(3x2−8)(4)(4x+3)2\frac{dy}{dx} = \frac{(6x)(4x+3) - (3x^2-8)(4)}{(4x+3)^2}
  7. Expand the terms in the numerator.

    dydx=24x2+18x−(12x2−32)(4x+3)2\frac{dy}{dx} = \frac{24x^2+18x - (12x^2-32)}{(4x+3)^2}
  8. Simplify the numerator by distributing the negative sign and combining like terms.

    dydx=24x2+18x−12x2+32(4x+3)2=12x2+18x+32(4x+3)2\frac{dy}{dx} = \frac{24x^2+18x - 12x^2+32}{(4x+3)^2} = \frac{12x^2+18x+32}{(4x+3)^2}

    The derivative is 12x2+18x+32(4x+3)2\boxed{\frac{12x^2+18x+32}{(4x+3)^2}}.

    ii) y=(3x3−8x2−1)6y = (3x^3-8x^2-1)^6

  9. Apply the chain rule, dydx=n[f(x)]n−1⋅f′(x)\frac{dy}{dx} = n[f(x)]^{n-1} \cdot f'(x), where f(x)=3x3−8x2−1f(x) = 3x^3-8x^2-1 and n=6n=6.

    First, find f′(x)f'(x): f′(x)=ddx(3x3−8x2−1)=9x2−16xf'(x) = \frac{d}{dx}(3x^3-8x^2-1) = 9x^2-16x.

    dydx=6(3x3−8x2−1)6−1⋅(9x2−16x)\frac{dy}{dx} = 6(3x^3-8x^2-1)^{6-1} \cdot (9x^2-16x)
  10. Simplify the exponent and rearrange the terms.

    dydx=6(9x2−16x)(3x3−8x2−1)5\frac{dy}{dx} = 6(9x^2-16x)(3x^3-8x^2-1)^5

    The derivative is 6(9x2−16x)(3x3−8x2−1)5\boxed{6(9x^2-16x)(3x^3-8x^2-1)^5}.

    iii) 4xy+y2=x2+24xy + y^2 = x^2+2

  11. Differentiate both sides of the equation with respect to xx.

    Remember to use the product rule for 4xy4xy and the chain rule for y2y^2.

    ddx(4xy)+ddx(y2)=ddx(x2)+ddx(2)\frac{d}{dx}(4xy) + \frac{d}{dx}(y^2) = \frac{d}{dx}(x^2) + \frac{d}{dx}(2) (4⋅y+4x⋅dydx)+(2y⋅dydx)=2x+0(4 \cdot y + 4x \cdot \frac{dy}{dx}) + (2y \cdot \frac{dy}{dx}) = 2x + 0 4y+4xdydx+2ydydx=2x4y + 4x\frac{dy}{dx} + 2y\frac{dy}{dx} = 2x
  12. Group terms containing dydx\frac{dy}{dx} on one side and other terms on the other side.

    4xdydx+2ydydx=2x−4y4x\frac{dy}{dx} + 2y\frac{dy}{dx} = 2x - 4y
  13. Factor out dydx\frac{dy}{dx} from the terms on the left side.

    dydx(4x+2y)=2x−4y\frac{dy}{dx}(4x + 2y) = 2x - 4y
  14. Solve for dydx\frac{dy}{dx} by dividing both sides by (4x+2y)(4x+2y).

    dydx=2x−4y4x+2y\frac{dy}{dx} = \frac{2x - 4y}{4x + 2y}
  15. Simplify the expression by dividing the numerator and denominator by 2.

    dydx=2(x−2y)2(2x+y)=x−2y2x+y\frac{dy}{dx} = \frac{2(x - 2y)}{2(2x + y)} = \frac{x - 2y}{2x + y}

    The derivative is x−2y2x+y\boxed{\frac{x - 2y}{2x + y}}.

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