Establish an appropriate plane rectangular coordinate system so that e=( 1, 0).
Let a = (x, y) and b = (m, n).
Ae=x,x= 1,be=m,m=2。
Then a = (1, y) and b = (2, n).
a-b=(- 1,y-n),ab=2+yn
So 1+(y-n)? =4
Get (y-n)? =3
So the question becomes (y-n)? =3, find the minimum value of 2+yn
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Solving the third year of high school: inequality method
(y-n)? =y? +n? -2yn
≥2|yn|-2yn,
So 3≥2|yn|-2yn
When yn > 0, it is obviously true.
When yn < 0,3 ≥-4yn, and yn≥-3/4, so 2+yn≥5/4, the minimum value is 5/4.
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Find the solution of senior one, y-n = √ 3, that is, y = n √ 3.
2+yn=2+n? √3n
The minimum value of the vertex coordinate formula of quadratic function is 5/4.