UPSKILL MATH PLUS

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Prove that \(\angle ACD = \angle A + \angle B\) using the properties of parallel lines.
 
 ext_proof.png
 
Proof:
 
Construct a line \(CE\) parallel to \(AB\).
 
ext_alt_proof.PNG
 
If \(AB \parallel CE\) and \(AC\) is the transversal, then \(∠A = ∠ACE\) .....(1) [Since ]
 
If \(AB \parallel CE\) and \(BD\) is the transversal, then \(∠B=∠ECD\) ......(2) [Since ]
 
\(∠ACD = ∠ACE + ∠ECD\) []
 
From equations (1) and (2), \(∠ACD = ∠A + ∠B\).
 
Hence, proved.