( 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

wait for