请教一道初三数学(与抛物线有关的
(1) 设y=a(x-x1)(x-x2),由A(k,0)(k<0),B(3,0)可知x1=k,x2=3,得:
OK=3OA=-3kC(0,-3k)代入y=a(x-x1)(x-x2)得:
a(0-k)(0-3)=-3k==>a=-1
==>y=-(x-k)(x-3)
y=-x^2+(3+k)x-3k;
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(2)由已知条件和已求条件得:
AC^2=AO^2+OC^2AC^2=k^2+9k^2=10k^2;
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作EF垂直于y轴,EG垂直于x轴,得...全部
(1) 设y=a(x-x1)(x-x2),由A(k,0)(k<0),B(3,0)可知x1=k,x2=3,得:
OK=3OA=-3kC(0,-3k)代入y=a(x-x1)(x-x2)得:
a(0-k)(0-3)=-3k==>a=-1
==>y=-(x-k)(x-3)
y=-x^2+(3+k)x-3k;
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(2)由已知条件和已求条件得:
AC^2=AO^2+OC^2AC^2=k^2+9k^2=10k^2;
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作EF垂直于y轴,EG垂直于x轴,得:
==>设E(x, y),则EF=OG=x, FO=EG=y,得:
ED^2=EF^2+FD^2ED^2=x^2+(y-t)^2
四边形ADEC是平行四边形,得:
AC=DEAC^2=DE^2,即:10k^2= x^2+(y-t)^2
化简得:x^2+y^2—2ty+t^2—10k^2=0……①
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同理:EF^2=CF^2+FE^2
即:EC^2=(-3k-y)^2+x^2,AD^2=AO^2+OD^2=k^2+t^2;
由EC=AOEC^2=AO^2,得:
(-3k-y)^2+x^2= k^2+t^2
化简得:x^2+y^2+6ky+8k^2-t^=0……②
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由②-①得:
18k^2+6ky+2yt-2t^2=0
18(k+y/6)^2-y/2-2(t-y/2)^2+y/2=0
k+y/6=0,t-y/2=0k=-y/6,t=y/2
t=-3k;
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(3)今晚或明天再答~~
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