Senior one mathematics compulsory 4 difficult problems (vector)

Solution: mainly use square, because the square of vector is equal to the square of module!

Vector AB= vector AO+ vector OB, and the squares of both sides: 16 = AO 2+OB 2+2 * vector A0* vector OB.

Vector AC= vector AO+ vector OC, the squares of both sides: 9 = ao 2+OC 2+2 * vector A0* vector OC.

Because OA, ob and oc are the radius of a circle, we can get ao 2 = ob 2 = oc 2.

Subtract the two expressions to get: 7=2* vector A0* vector OB-2* vector A0* vector OC,

That is, 7=2* vector A0* (vector OB- vector OC),

7=2* vector A0* vector CB,

-7= 2* vector A0* vector BC

So vector A0* vector BC =-7/2.

Therefore, vector 0A* vector BC =7/2.

I hope it helps you!