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In triangle PQR, PQ = 41.6 m, PR = 70 m, and angle PQR = 105°. Calculate angle QPR and the area of triangle PQR.

Mathematics

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3 parts
i

40.0∘40.0^\circ

ii

934.8 m2934.8 \text{ m}^2

iii

26.7 m26.7 \text{ m}

Step 1: Calculate angle ∠PRQ\angle PRQ.
We use the Sine Rule:

PQsin⁡(∠PRQ)=PRsin⁡(∠PQR)\frac{PQ}{\sin(\angle PRQ)} = \frac{PR}{\sin(\angle PQR)}

Substitute the given values: PQ=41.6 mPQ = 41.6 \text{ m}, PR=70 mPR = 70 \text{ m}, ∠PQR=105∘\angle PQR = 105^\circ.

41.6sin⁡(∠PRQ)=70sin⁡105∘\frac{41.6}{\sin(\angle PRQ)} = \frac{70}{\sin 105^\circ}

Rearrange to solve for sin⁡(∠PRQ)\sin(\angle PRQ):

sin⁡(∠PRQ)=41.6×sin⁡105∘70\sin(\angle PRQ) = \frac{41.6 \times \sin 105^\circ}{70}

Calculate sin⁡105∘≈0.9659258\sin 105^\circ \approx 0.9659258:

sin⁡(∠PRQ)=41.6×0.965925870\sin(\angle PRQ) = \frac{41.6 \times 0.9659258}{70} sin⁡(∠PRQ)=40.2016132870\sin(\angle PRQ) = \frac{40.20161328}{70} sin⁡(∠PRQ)≈0.57430876\sin(\angle PRQ) \approx 0.57430876

Now, find ∠PRQ\angle PRQ:

∠PRQ=arcsin⁡(0.57430876)\angle PRQ = \arcsin(0.57430876) ∠PRQ≈35.05∘\angle PRQ \approx 35.05^\circ

Part (i): Calculate angle QPR.
The sum of angles in a triangle is 180∘180^\circ.

∠QPR+∠PQR+∠PRQ=180∘\angle QPR + \angle PQR + \angle PRQ = 180^\circ ∠QPR=180∘−∠PQR−∠PRQ\angle QPR = 180^\circ - \angle PQR - \angle PRQ

Substitute the values:

∠QPR=180∘−105∘−35.05∘\angle QPR = 180^\circ - 105^\circ - 35.05^\circ ∠QPR=39.95∘\angle QPR = 39.95^\circ

Rounding to one decimal place:

∠QPR≈40.0∘\angle QPR \approx \boxed{40.0^\circ}

Part (ii): Calculate the area of triangle PQR.
The area of a triangle can be calculated using the formula:

Area=12absin⁡C\text{Area} = \frac{1}{2}ab\sin C

Using sides PQPQ, PRPR and the included angle ∠QPR\angle QPR:

Area=12×PQ×PR×sin⁡(∠QPR)\text{Area} = \frac{1}{2} \times PQ \times PR \times \sin(\angle QPR)

Substitute the values: PQ=41.6 mPQ = 41.6 \text{ m}, PR=70 mPR = 70 \text{ m}, ∠QPR=39.95∘\angle QPR = 39.95^\circ.

Area=12×41.6 m×70 m×sin⁡(39.95∘)\text{Area} = \frac{1}{2} \times 41.6 \text{ m} \times 70 \text{ m} \times \sin(39.95^\circ)

Calculate sin⁡(39.95∘)≈0.64207\sin(39.95^\circ) \approx 0.64207:

Area=12×41.6×70×0.64207\text{Area} = \frac{1}{2} \times 41.6 \times 70 \times 0.64207 Area=20.8×70×0.64207\text{Area} = 20.8 \times 70 \times 0.64207 Area=1456×0.64207\text{Area} = 1456 \times 0.64207 Area≈934.78 m2\text{Area} \approx 934.78 \text{ m}^2

Rounding to one decimal place:

Area≈934.8 m2\text{Area} \approx \boxed{934.8 \text{ m}^2}

Part (iii): Calculate the shortest distance from Q to PR.
The shortest distance from a vertex to the opposite side is the altitude (height).
Let hh be the shortest distance from Q to PR. The base is PRPR.
The area of a triangle can also be calculated as:

Area=12×base×height\text{Area} = \frac{1}{2} \times \text{base} \times \text{height} Area=12×PR×h\text{Area} = \frac{1}{2} \times PR \times h

We know the Area from Part (ii) and PR=70 mPR = 70 \text{ m}.

934.78 m2=12×70 m×h934.78 \text{ m}^2 = \frac{1}{2} \times 70 \text{ m} \times h 934.78=35×h934.78 = 35 \times h

Rearrange to solve for hh:

h=934.7835h = \frac{934.78}{35} h≈26.708 mh \approx 26.708 \text{ m}

Rounding to one decimal place:

h≈26.7 mh \approx \boxed{26.7 \text{ m}}
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