The y-axis divides the join of the points A(a, b) and Bla₂, b₂) in the ratio

It seems like your question is incomplete. However, I can tell you that if the y-axis (x=0) divides the line segment joining the points A(a, b) and B(a₂, b₂) in the ratio m:n, then the x-coordinate of the point of division can be found using the formula for section formula in coordinate geometry.

The formula is:

x = (ma₂ + na) / (m + n)

Since the y-axis is the line where x=0, for the y-axis to divide the line segment AB in the ratio m:n, the x-coordinate of the point of division should be 0. So, we set x=0 in the formula and solve for the ratio:

0 = (ma₂ + na) / (m + n)

This equation can be solved further to find the values of m and n, which represent the ratio in which the y-axis divides the line segment AB.