式子一:∠P+1/2∠B=1/2∠A+28°
式子二:∠P+1/2∠A=1/2∠B+32°
两式子相加得到:2∠P+1/2∠A+1/2∠B=1/2∠A+1/2∠B+28°+32°
2∠P=60°
∠P=30°
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