Lines AB
and
CD
are straight lines. Find x and y. Give reasons to justify your solutions.

x = 18

y = 54°

Step-by-step explanation:

m<MON = 90° (given)

m<MOA = 72° (given)

m<AON + m<MOA = m<MON (Angle Addition Postulate)

m<AON + 72° = 90° (Substitution)

Subtract 72° from each side

m<AON = 90° - 72°

m<AON = 18°

m<AOD = 18° + 2x

m<BOC = 3x

m<AOD = m<BOC (vertical angles)

18 + 2x = 3x (Substitution)

Subtract 2x from each side

18 = 3x - 2x

18 = x

x = 18.

72° + y + 3x = 180° (angles on a straight line)

Plug in the value of x

72 + y + 3(18) = 180

72 + y + 54 = 180

126 + y = 180

Subtract 126 from both sides

y = 54