【高一数学】21题怎么做？
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(1)
DA
= -CD + CA
=-CD - (AB+BC)
=(2,3) - ( (3,2)+(x,y) )
=(-1-x, 1-y)
BC//DA
BC = kDA
x/y = (-1-x)/(1-y)
x(1-y) = -y(1+x)
x-xy = -y -xy
x=-y
(2)
AC = AB+ BC = (3+x, 2+y)
BD =BC + CD =(x-2, y-3)
AC.BD =0
(x+3)(x-2) + (y+2)(y-3) =0
x^2 +x -6 +(y^2-y-6) =0
x^2 +x -6 +(x^2+x-6) =0 ( x= -y)
x^2+x-6=0
(x+3)(x-2) = 0
x=-3 or 2
x=-3, y=3
x=2, y = -2
(x,y)= (-3,3) or (2,-2)
DA
= -CD + CA
=-CD - (AB+BC)
=(2,3) - ( (3,2)+(x,y) )
=(-1-x, 1-y)
BC//DA
BC = kDA
x/y = (-1-x)/(1-y)
x(1-y) = -y(1+x)
x-xy = -y -xy
x=-y
(2)
AC = AB+ BC = (3+x, 2+y)
BD =BC + CD =(x-2, y-3)
AC.BD =0
(x+3)(x-2) + (y+2)(y-3) =0
x^2 +x -6 +(y^2-y-6) =0
x^2 +x -6 +(x^2+x-6) =0 ( x= -y)
x^2+x-6=0
(x+3)(x-2) = 0
x=-3 or 2
x=-3, y=3
x=2, y = -2
(x,y)= (-3,3) or (2,-2)
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