(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
The Formula of interal division is
\((\frac{mx_2 +nx_1}{m+n},\frac{my_2 +ny_1}{m+n})\)
Hence, our reason (R) is true.
Let x-axis divides line segment joining points A(2,-3) and B(5,6) internally in the ratio K : 1.

∴ y -coordinate of that point should be zero because y-coordinate of any point on x-axis is zero.
∴ \(\frac{6k-3}{k+1}=0\)
(By putting m = k, n = 1, y2 = 6 & y, = -3 in equation (1))
⇒ 6k - 3 = 0
⇒ k = 3/6 = 1/2
⇒ k/1 = 1/2
⇒ k : 1 = 1 : 2
Hence, x-axis divides line segment joining points (2,-3) & (5,6) internally in the ratio 1 : 2.
Hence, our assertion and reason both are true and reason is correct explanation of assertion.