如图,抛物线y=x 2 +bx+c与x轴交于A(-1,0)、B(3,0)两点。 (1)求该抛物线的解析式; 如图,抛物线y=x 2 +bx+c与x轴交于A(﹣1,0)和...
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解:①将点A(-1,0), B(3,0)代入y=x 2 +bx+c中得: ②解:设p点的纵坐标为t ③存在 ∵点A,B关于抛物线的对称轴对称∴连接BC与对称轴的交点Q就能使 周长最小 设直线BC解析式为:y=kx+b,又∵C(0,-3) B(3,0) ∴y=x-3 又∵抛物线对称轴为x=1 ∴Q(1,-2) |