Question

Prove that if$A_1,A_2,\dots ,A_n$ and B are sets, then

$\begin{array}{r}\left(A_1-B\right)\cap \left(A_2-B\right)\cap \dots \cap \left(A_n-B\right)\\ =\left(A_1\cap A_2\cap ,\dots \cap A_n\right)-B\end{array}$

Short answer

$\begin{array}{r}\left(A_1-B\right)\cap \left(A_2-B\right)\cap \dots \cap \left(A_n-B\right)\\ =\left(A_1\cap A_2\cap ,\dots \cap A_n\right)-B\end{array}$

Step-by-step solution

Step: 1

If n=1,

$A_1-B=A_1-B$

it is true for n=1.

Step: 2

Let P(k) be true.

$\begin{array}{r}\left(A_1-B\right)\cap \left(A_2-B\right)\cap \dots \cap \left(A_k-B\right)\\ =\left(A_1\cap A_2\cap ,\dots \cap A_k\right)-B\end{array}$

We need to prove that P(k+1) is true.

Step: 3

$\begin{array}{r}\left(A_1-B\right)\cap \left(A_2-B\right)\cap \dots \cap \left(A_k-B\right)\cap \left(A_{k+1}-B\right)\\ =\left(A_1\cap A_2\cap \dots \cap A_k\right)-B\left(\cap A_{k+1}-B\right)\\ \left.\left.=\left(A_1\cap A_2\cap \dots \cap A_k\right)\cap A_{k+1}\right)-B\right)\\ =\left(A_1\cap A_2\cap ,\dots \cap A_k\cap A_{k+1}\right)-B\end{array}$

Hence it is true for P(k+1).