6. Congruence among Right Angled triangles

 CONGRUENCE OF TRIANGLES
    Two triangles are congruent if pairs of corresponding sides and corresponding angles are congruent.

We can superimpose ∆∆  so as to cover it exactly. 
During superimposing, side AB falls on side PQ, BC falls on side QR and AC falls on PR. Vertex A falls on P, B falls on Q and C fall on R. If two triangles are congruent then corresponding parts (i.e. angles and  sides) that match one another are equal. Thus, in these two congruent triangles, we have;