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Lines And Angles

Question
CBSEENMA9002372

In figure, POQ is a line. Ray OR is perpendicular to line PQ. OS is another ray lying between rays OP and OR. Prove that  

angle ROS equals 1 half left parenthesis angle QOS minus angle POS right parenthesis


Solution

∵ Ray OR is perpendicular to line PQ.
∴ ∠QOR = ∠POR = 90°    ...(1)
∠QOS = ∠QOR + ∠ROS    ...(2)
∠POS = ∠POR - ∠ROS    ...(3)
From (2) and (3),
∴ ∠QOS - ∠POS = (∠QOR - ∠POR) + 2∠ROS = 2∠ROS | Using (1)
rightwards double arrow space angle ROS equals 1 half left parenthesis angle QOS minus angle POS right parenthesis