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已知直线y=kx+b与x轴交于点P与直线y=-x+5的交点Q的纵坐标为4PQ=2√5若直线y=-x+5与x轴交于点M求S

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已知直线y=kx+b与x轴交于点P与直线y=-x+5的交点Q的纵坐标为4PQ=2√5若直线y=-x+5与x轴交于点M求S⊿MPQ的值
已知直线y=kx+b与x轴交于点P与直线y=-x+5的交点Q的纵坐标为4PQ=2√5若直线y=-x+5与x轴交于点M求S
解y = 0,y=kx+b,P(-b/k,0)
解y=kx+b,y=-x+5,Q((5-b)/(k+1),(5k+b)/(k+1))
解y = 0,y= -x + 5,M(5,0)
Q的纵坐标为4:(5k+b)/(k+1) = 4,k = 4-b
P(b/(b-4),0)
Q(1,4)
|PQ|² = (2√5)² = 20 = [b/(b-4) -1]² + (0-4)²
[b/(b-4) -1]² = 4
b/(b-4) -1 = ±2
b = 6或b = 2
P(3,0)或(-1,0)
(1) b = 6,P(3,0)
|PM| = |5 - 3| = 2
PM上的高为Q的纵坐标4
S⊿MPQ = (1/2)*2*4 = 4
(2) b = 2,P(-1,0)
|PM| = |5 - (-1)| = 6
PM上的高为Q的纵坐标4
S⊿MPQ = (1/2)*6*4 = 12