In the known triangle ABC, AB=a, AC=b, when ab <0 or ab=0, try to judge the shape of △ABC (related to the number product of plane vector)

In the known triangle ABC, AB=a, AC=b, when ab <0 or ab=0, try to judge the shape of △ABC (related to the number product of plane vector)

Vector AB·Vector AC=|AB AC|cosA <0
So cosA <0, A is obtuse angle,△ABC is obtuse angle triangle
Vector AB·Vector AC=|AB AC|cosA=0
So cosA=0, A is a right angle,△ABC is a right triangle

In triangle ABC, AB =3 below the root, A =45 degrees, C =75 degrees, find BC. Use the plane vector method,

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Given vector a =3, vector b =2, vector a - vector b = root number 7, then vector a · vector b

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If the plane vector b is parallel to the vector a=(2,1), and |b|=2 roots 5, then b= Uh. 。。 All of a sudden I understand again. Please ignore this question. 。。 。

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Given vector a=(root number 3,-1), vector b=(1, root number 3), if vector A*vector C=vector B*vector C, coordinate of vector C of root 2. It's better to ask for help than to solve M=1. = Given vector a=(root number 3,-1), vector b=(1, root number 3), if vector A*vector C=vector B*vector C, coordinate of vector C of root 2. It's better to beg others than to beg yourself to solve M=1. =

Let the coordinate of vector c be (x, y), then let x+y=2
Set (root 3-1) x=(root 3+1) y to two
Concurrent x-square =1/(4-2 root #3)=1/(root #3-1) square
So x1=1/(root 3-1), y1=1/(root 3+1)
X2=1/(1- root 3), y2=-1/(root 3+1)
That's what you want.

If the vectors a and b are non-zero and satisfy |vector a+vector b|=|vector a-vector b|=2|vector b|, prove:|vector b|=3 times of the root number |vector If vectors a and b are non-zero and satisfy |vector a+vector b|=|vector a-vector b|=2|vector b|, prove:|vector b|=3 times of root number |vector If vectors a and b are non-zero and satisfy |vector a+vector b|=|vector a-vector b|=2|vector b|, prove:|vector b|=3 times of the root number |vector

| Vector a + vector b |=| vector a - vector b | square a + square b +2a * b = square a + square b -2a * b = square a =0, so vector a is perpendicular to vector b | vector a + vector b |=| vector a - vector b |=2| vector b | so the angle between (a + b) and a is 30°.Therefore:| vector a |=3 times root number | vector b | is:| vector b |=3...