Answer:
M∠DEC equals 123º.
Explanation:
The sum of a triangle's three angles always equal 180º. The exterior angle, x, equals the two non-adjacent interior angles.
180 - {(x - 45)+(x - 12)} = m∠DEC
m∠DEC + x = 180
(x - 45) + (x - 12) = x
Solving for x:
(x - 45) + (x - 12) = x
x - 45 + x - 12 = x Remove parenthesis
2x - 57 = x Combine like terms
2x = x + 57 Add 57 to both sides
x = 57 Subtract x from both sides
Finding m∠D:
x - 45 = ?
57 - 45 = 12º
Finding m∠C:
x - 12 = ?
57 - 12 = 45º
** (Checking x: 12 + 45 = 57) **
Finding m∠DEC:
AC is a straight line, and because straight lines are equivalent to 180º, we subtract 57 from 180:
180 - 57 = 123º
Hope this helps,
❤A.W.E.S.W.A.N.❤