Question 1 Construct an angle of90∘at the initial point of a given ray and justify the construction.
Open in App
Solution
Steps to construct an angle of 90∘ (i) Let us take a ray PQ with initial point P and draw an arc of some radius taking point P as its centre, which intersects PQ at R. (ii) Taking R as the centre and with the same radius as before, draw an arc intersecting the previously drawn arc at S. (iii) Taking S as the centre and with the same radius as before, draw an arc intersecting the arc at T(see figure). (iv) Taking S and T as centre, draw an arc of same radius to intersect each other at U. (v) Join PU, which is the required ray that makes an angle of 90∘with the given ray PQ.
Justification We can justify the construction if we can prove ∠UPQ=90∘ For this, join PS and PT.
We have,∠SPQ=∠TPS=60∘ In (iii) and (iv) steps of this construction, PU was drawn as the bisector of∠TPS. ∴∠UPS=12×60∘=30∘ Also, ∠UPQ=∠SPQ+∠UPS =60∘+30∘ =90∘