If ∠ a = 4 ∠ B in the isosceles triangle ABC is known, the degree of ∠ C can be obtained
∵∠a=4∠b
ABC is an isosceles triangle
Therefore, B = - C or a = - C
∠a+∠b+∠c=180°
If ∠ B = ∠ C, substitute ∠ C = 30 °
If ∠ a = ∠ C, substitute ∠ C = 80 °
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