Because all 3 sides are given for both triangles you can use the SSS theorem
First you need to know the definition of a complementary angle. That means that two angles add up to 90 degrees, or a right angle.
To find an angle complementary to a 78 degree angle, you need to subtract 78 from 90.
90 - 78 = 12
Only the second one
when diameter is 4 r=2
so 2pi*2=2²*pi the first is circumference the second area
