Q.PQRS is a cyclic quadrilateral in which side QR is extended up to point T. If the measures of angles ∠SRQ and ∠SRT are in the ratio 4:5, then find the measures of ∠SPQ and ∠SRQ.

∠SRQ : ∠SRT = 4 : 5 = \(\frac{4}{9} : \frac{5}{9}\) [because 4 + 5 = 9] Also, ∠SRQ + ∠SRT = 180° [because RS is a straight line standing on QT at point R] ∴ ∠SRQ = \(180^\circ \times \frac{4}{9} = 80^\circ\) And, ∠SPQ = \(180^\circ - ∠SRQ = 180^\circ - 80^\circ = 100^\circ\) ∴ ∠SPQ = 100° and ∠SRQ = 80°
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