see complementary angles means their addition would always be equal to 90° so here given is 1 and 2 are complementary so 1 + 2 = 90° NOW here the angle adjacent to 2 is a right angled triangle and the line bisecting and dividing those 2. 1 and 2 angle is a straight and linear thus it will be angle 2 + that right angle + angle 3 = 180 we already know that second one is right angled thus angle 2 + angle 3 = 180-90 and hence 2+3 = 90 they are complementary too
