We are given that $AD \cong AE$, $BA || CE$, $CB || DA$, and $m\angle DAE = 54^\circ$. We need to find $m\angle BCD$.

GeometryAnglesTrianglesParallel LinesTrapezoidsSupplementary AnglesIsosceles Triangle
2025/3/10

1. Problem Description

We are given that ADAEAD \cong AE, BACEBA || CE, CBDACB || DA, and mDAE=54m\angle DAE = 54^\circ. We need to find mBCDm\angle BCD.

2. Solution Steps

Since ADAEAD \cong AE, ADE\triangle ADE is an isosceles triangle. Therefore, ADEAED\angle ADE \cong \angle AED. Let x=mADE=mAEDx = m\angle ADE = m\angle AED. The sum of the angles in ADE\triangle ADE is 180180^\circ.
mDAE+mADE+mAED=180m\angle DAE + m\angle ADE + m\angle AED = 180^\circ
54+x+x=18054^\circ + x + x = 180^\circ
2x=180542x = 180^\circ - 54^\circ
2x=1262x = 126^\circ
x=1262=63x = \frac{126^\circ}{2} = 63^\circ
So, mADE=mAED=63m\angle ADE = m\angle AED = 63^\circ.
Since CBDACB || DA, ABCDABCD is a trapezoid, but we don't know if it's an isosceles trapezoid. Since BACEBA || CE, ABCEABCE is a trapezoid. Since CBDACB || DA, BCD\angle BCD and ADC\angle ADC are supplementary angles. Also, since BACEBA || CE, ABC\angle ABC and BCE\angle BCE are supplementary angles.
mBCD+mADC=180m\angle BCD + m\angle ADC = 180^\circ
mADC=mADE=63m\angle ADC = m\angle ADE = 63^\circ.
Since CBDACB || DA, the quadrilateral ABCDABCD is a trapezoid. Furthermore, we know BACEBA || CE. Thus, ABC\angle ABC and BCE\angle BCE are supplementary, so their sum is 180180^\circ. Also, ADBCAD || BC, so ADC\angle ADC and BCD\angle BCD are supplementary, so their sum is 180180^\circ.
Since mADC=63m\angle ADC = 63^\circ, we have
mBCD+63=180m\angle BCD + 63^\circ = 180^\circ
mBCD=18063=117m\angle BCD = 180^\circ - 63^\circ = 117^\circ

3. Final Answer

mBCD=117m\angle BCD = 117^\circ

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