Question 1027626
If  5x–2y=3 and x+y=a are to intersect at the y-axis, the x-coordinate of the intersection point must be 0. By using Cramer's rule, the x-coordinate is given by 

{{{x = abs(matrix(2,2,a,1,3,-2))/abs(matrix(2,2,1,1,5,-2)) = (2a+3)/7}}}.

Hence, {{{(2a+3)/7 = 0}}}, and a = -3/2.