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n △ABC, D is a point on side AC such that BD=DC and ∠BCD measures 70∘. What is the degree measure of ∠ADB?

Sagot :

Since BD = DC, and ∠BCD whose measure is 70° is a base angle, therefore:

m∠BCD = m∠DBC
      70°  =     70°

The measure ∠BDC is:
m∠BDC = 180° - (m∠BCD + m∠DBC)
m∠BDC = 180° - (70° + 70°)
m∠BDC = 180 - (140°)
m∠BDC = 40°

∠BDC and ∠ADB are supplementary angles. 
m∠ADB = 180° - m∠BDC
m∠ADB = 180° - 40°
m∠ADB = 140°

The degree measure of ∠ADB is 140°.
    

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