Which of the following vectors are orthogonal to (1,5)? check all that apply a. (-2,5) b. (10,-2) c. (-1,-5) d. (-5,1)

We know that
If the scalar product of two vectors is zero, both vectors are orthogonal

A. (-2,5)
(-2,5)*(1,5)> -2*1+5*5=23> are not orthogonal 

B. (10,-2)
(10,-2)*(1,5)> 10*1-2*5=0> are  orthogonal 

C. (-1,-5)
(-1,-5)*(1,5)> -1*1-5*5=-26> are not orthogonal 

D. (-5,1)
(-5,1)*(1,5)> -5*1+1*5=0> are  orthogonal 

the answer is 
B. (10,-2) and D. (-5,1)  are  orthogonal  to  (1,5)