Planes M and N intersect at line d. Lines a, b, and e are on plane M. Line a is vertical and forms a right angle with line d. Line b is diagonal and goes up and to the right. Line e is at the top of the plane and is close to being horizontal. Line c is on plane N and is goes slightly up and to the right. Why are lines e and c skew lines? They lie in different planes and will never intersect. They lie in the same plane but will never intersect. They lie in different planes but will intersect if a plane is drawn to contain both lines. They lie in different planes and will be parallel if a plane is drawn to contain both lines.

according to the triangle sum theorem, all the angles in a triangle must add up to 180 degrees. if we know one angle is already 90, we do 180-90=90. the other 2 angles must add up to 90, exactly.

step-by-step explanation:

a 4/6 = 9/12   not proportional

step-by-step explanation:

to find which are not proportional, we can use cross products

if it is true, they are proportional.   if it is not true, they are not proportional.

a 4/6 = 9/12

4* 12 = 6*9

48 = 54

not this is not proportional  

b 2/3 = 12/18  

2* 18 = 3 * 12

36 = 36

this is proportional

c 5/4 = 10/8  

5*8 = 4*10

40 = 40

this is proportional

d 7/5 = 35/25

7*25 = 5 * 35

175 = 175

is proportional