Question

out of the four angles formed by two intersecting lines one is 90 degree prove that the other 3 angles will be 90

Answer 1

method 1 )in 2 intersecting lines each is a straight angle (180°) . so if one angle is 90 then the one adjacent to it will be also 90° because it is a straight and thus forms linear pair . then the next angle adjacent to it will be taken out by the same method and next to next one also by same method.

method 2 )as mentioned above about the straight angle you can take out by
straight angle + straight angle = 360°
so
90+90+90+90= 360