( 1)? ∫A(- 1,-2)B(2,3)C(-2,- 1)
∴? Vector ab = (2 2,3)-? (- 1,-2)=? (3,? 5)
Vector AC=(-2,-1)-? (- 1,-2)=? (- 1,? 1)
Diagonal vector advertising? =? Vector AB? +? Vector communication? =? (3,? 5)+? (- 1,? 1)=? (2,? 6)
Diagonal vector BC? =? Vector communication? -Vector AB? =? (- 1,? 1)-? (3,? 5)=? (-4,? -4)
So what? What are the lengths of the two diagonals? l? Vector ADl? =? √(2? +6? )=√40? =? 2√ 10
l? Vector BC? l? =? √[(-4)? +(-4)? ]? =? √32? =? 4√2
(2)? Vector AB? -t? Vector OC? =? (3,? 5)-? t? (-2,? - 1)
=(3,? 5)-(-2t,? -t? )
=? (3+2t,5+t? )
∵ (vector AB? -t? Vector OC)? ⊥? Vector OC
∴-2(3+2t)-? (t+5)=? 0
4t? +6? +t? +5? =0
5t? +? 1 1? =0
t? =? -? 1 1/5
This is the basic question type of vector: the basic knowledge used is:
1.? Geometric expression and coordinate expression of vector addition and subtraction;
2.? Necessary and Sufficient Conditions for Verticality of Vector (Coordinate Form)
3.? Calculation formula of vector modulus
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