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If PQRS is a rhombus such that ∠PRQ=40°, then ∠PSQ is:
60°
50°
40°
45°
50°
In a rhombus, diagonals bisect the opposite angles, and the triangle formed by two sides and a diagonal is isosceles; specifically, the alternate angles subtended by the sides at the vertices are equal.
PQRS is a rhombus and \angle PRQ = 40°.
∠PSQ=∠PRQ
In a rhombus, diagonals bisect the opposite angles, and the triangle formed by two sides and a diagonal is isosceles; specifically, the alternate angles subtended by the sides at the vertices are equal.
Students often incorrectly assume \angle PSQ is complementary to \angle PRQ (i.e., 50°) because they mistake the triangle for a right triangle, forgetting that only the intersection of diagonals forms right angles.
Analyze Rhombus Properties
In a rhombus PQRS, all sides are equal (PQ=QR=RS=SP). The diagonal PR divides the rhombus into two congruent triangles △PQR and △PSR.
PQ=QR=RS=SP
Use Symmetry of Rhombus
Because PQ∥SR and PS∥QR, the diagonal PR acts as a transversal. By alternate interior angles, ∠QRP=∠SPR. Due to the property of rhombus diagonals bisecting angles, ∠PSQ=∠PRQ.
∠PSQ=∠PRQ=40°
Final Verification
Given ∠PRQ=40°, by the property that diagonals of a rhombus create equal angles at the vertices due to congruent triangles △PQS and △RQS, we confirm the value.
∠PSQ=40°
C is correct because in a rhombus, the diagonals bisect the vertex angles and the triangles formed are symmetric, leading to ∠PSQ=∠PRQ=40°.
Always remember that a rhombus is a special type of parallelogram where diagonals are perpendicular bisectors; utilize these properties to solve angle geometry questions rapidly.