Here are the steps to construct △PQR and calculate its angles.
Given side lengths:
PQ=8 cm
QR=11 cm
PR=10 cm
Step 1: Check if the triangle can be constructed.
We apply the Triangle Inequality Theorem: the sum of any two sides must be greater than the third side.
- PQ+QR>PR⇒8+11=19 cm. Since 19>10, this condition is met.
- PQ+PR>QR⇒8+10=18 cm. Since 18>11, this condition is met.
- QR+PR>PQ⇒11+10=21 cm. Since 21>8, this condition is met.
Since all conditions are met, the triangle can be constructed.
Step 2: Describe the construction steps.
- Draw a line segment PQ of length 8 cm.
- With P as the center, use a compass to draw an arc with a radius of 10 cm (the length of PR).
- With Q as the center, use a compass to draw an arc with a radius of 11 cm (the length of QR).
- The point where these two arcs intersect is point R.
- Draw line segments PR and QR to complete △PQR.
Step 3: Calculate the angles using the Law of Cosines.
Let p=QR=11 cm, q=PR=10 cm, and r=PQ=8 cm.
To find ∠P:
cosP=2qrq2+r2−p2
cosP=2⋅10⋅8102+82−112
cosP=160100+64−121
cosP=16043
P=arccos(16043)
P≈74.38∘
To find ∠Q:
cosQ=2prp2+r2−q2
cosQ=2⋅11⋅8112+82−102
cosQ=176121+64−100
cosQ=17685
Q=arccos(17685)
Q≈61.05∘
To find ∠R:
cosR=2pqp2+q2−r2
cosR=2⋅11⋅10112+102−82
cosR=220121+100−64
cosR=220157
R=arccos(220157)
R≈44.57∘
The sum of the angles is 74.38∘+61.05∘+44.57∘=180.00∘.
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