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The diagram shows a sector of a circle with centre O, radius 8 cm and sector angle 165 degrees. (a) Calculate the total perimeter of the sector. (b) The surface area of a sphere is the same as the area of the sector. Calculate the radius of the sphere.

Mathematics

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Answers

2 parts
a

39.0 cm39.0 \text{ cm}

b

2.71 cm2.71 \text{ cm}

Step-by-step solution

5 steps

Here are the solutions to the problems from the image:

18. (d) Adam earned $36 515 in 2019. This was an increase of 9% on his earnings in 2018. Work out his earnings in 2018.

Step 1: Understand the relationship between 2018 and 2019 earnings.
If Adam's earnings increased by 9% in 2019, his 2019 earnings represent 100% + 9% = 109% of his 2018 earnings.
Let E2018E_{2018} be his earnings in 2018.

E2019=E2018×(1+0.09)E_{2019} = E_{2018} \times (1 + 0.09) E2019=E2018×1.09E_{2019} = E_{2018} \times 1.09

Step 2: Calculate his earnings in 2018.
We are given E_{2019} = \36,515. $$\36,515 = E_{2018} \times 1.09 E_{2018} = \frac{$36,515}{1.09} E_{2018} = $33,500$$ Adam's earnings in 2018 were \boxed{\33,500}$.

19. The diagram shows a sector of a circle with centre O, radius 8 cm and sector angle 165°.

Part a· 2 steps

Calculate the total perimeter of the sector.

  1. Calculate the length of the arc.

    The formula for arc length LL is L=θ360∘×2πrL = \frac{\theta}{360^\circ} \times 2\pi r.
    Given θ=165∘\theta = 165^\circ and r=8r = 8 cm.

    L=165360×2×π×8L = \frac{165}{360} \times 2 \times \pi \times 8 L=165360×16πL = \frac{165}{360} \times 16\pi L=1124×16πL = \frac{11}{24} \times 16\pi L=11×23×πL = \frac{11 \times 2}{3} \times \pi L=223π cmL = \frac{22}{3}\pi \text{ cm} L≈23.038 cmL \approx 23.038 \text{ cm}
  2. Calculate the total perimeter of the sector.

    The perimeter of the sector is the sum of the arc length and two radii.
    Perimeter P=L+2rP = L + 2r

    P=223π+2(8)P = \frac{22}{3}\pi + 2(8) P=223π+16P = \frac{22}{3}\pi + 16 P≈23.038+16P \approx 23.038 + 16 P≈39.038 cmP \approx 39.038 \text{ cm}

    Rounding to one decimal place:

    P≈39.0 cmP \approx 39.0 \text{ cm}

    The total perimeter of the sector is 39.0 cm\boxed{39.0 \text{ cm}}.

Part b

2.71 cm2.71 \text{ cm}

The surface area of a sphere is the same as the area of the sector. Calculate the radius of the sphere. [The surface area, A, of a sphere with radius r is A=4πr2A = 4\pi r^2]

  1. Calculate the area of the sector.

    The formula for the area of a sector AsectorA_{sector} is Asector=θ360∘×πr2A_{sector} = \frac{\theta}{360^\circ} \times \pi r^2.
    Given θ=165∘\theta = 165^\circ and r=8r = 8 cm.

    Asector=165360×π×82A_{sector} = \frac{165}{360} \times \pi \times 8^2 Asector=165360×64πA_{sector} = \frac{165}{360} \times 64\pi Asector=1124×64πA_{sector} = \frac{11}{24} \times 64\pi Asector=11×83×πA_{sector} = \frac{11 \times 8}{3} \times \pi Asector=883π cm2A_{sector} = \frac{88}{3}\pi \text{ cm}^2 Asector≈92.153 cm2A_{sector} \approx 92.153 \text{ cm}^2
  2. Set the area of the sector equal to the surface area of the sphere.

    Let rsr_s be the radius of the sphere. The surface area of the sphere is Asphere=4πrs2A_{sphere} = 4\pi r_s^2.

    Asphere=AsectorA_{sphere} = A_{sector} 4πrs2=883π4\pi r_s^2 = \frac{88}{3}\pi
  3. Solve for the radius of the sphere, rsr_s.

    Divide both sides by π\pi:

    4rs2=8834r_s^2 = \frac{88}{3}

    Divide both sides by 4:

    rs2=883×4r_s^2 = \frac{88}{3 \times 4} rs2=8812r_s^2 = \frac{88}{12} rs2=223r_s^2 = \frac{22}{3} rs=223r_s = \sqrt{\frac{22}{3}} rs≈7.33333r_s \approx \sqrt{7.33333} rs≈2.7080 cmr_s \approx 2.7080 \text{ cm}

    Rounding to two decimal places (or 3 significant figures):

    rs≈2.71 cmr_s \approx 2.71 \text{ cm}

    The radius of the sphere is 2.71 cm\boxed{2.71 \text{ cm}}.

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