Let A(x , 2 , -1) ,B(0, y , 1) ,C(3 , 4 , -2) , AB=AC and ABC is isosceles right triangle. Find x and y ?

we have number from 1 to 2014. If we underline the number that divide by 3 and 4, how many pattern of two underlines that next to each other as example?(1,2,3,4,5,6,7,8,9,10,...,2014).

From 1 to 1000, how many time we use "5"?

Let a(1)=916 , a(2)=935 , a(3)=713  , a(4)=845  , a(5)=274  , a(6)=914 ,a(7)=255 . Find formula a(n)= ? ,n=1,2,3,....

Let OA=OB=OC=R=3,AB=3√2 and BC=2√2 .Find AC?