Then the number of elements in the set {(n, m) : n, m ∈ { 1, 2….., 10} and nAn + mBm = I} is _______.
The correct answer is : 1
A2 = A and B2 = BR
nA + mB = I,
So, 2n – m = 1, –n + m = 0, 2m – n = 1
So, (m, n) = (1, 1)

Two circular discs of radius \(10\) cm each are joined at their centres by a rod, as shown in the figure. The length of the rod is \(30\) cm and its mass is \(600\) g. The mass of each disc is also \(600\) g. If the applied torque between the two discs is \(43\times10^{-7}\) dyne·cm, then the angular acceleration of the system about the given axis \(AB\) is ________ rad s\(^{-2}\).

Sets are of various types depending on their features. They are as follows: