### Video Transcript

Factorise fully 100π₯ squared minus 121π¦ squared.

As both terms in the expression are square numbers, we can use the difference of two squares identity. The difference of two squares identity tells us that π squared minus π squared is equal to π plus π multiplied by π minus π.

In this case, π squared is equal to 100π₯ squared. Square rooting both sides of this equation gives us π is equal to 10π₯, as the square root of 100π₯ squared is 10π₯. In the same way, π squared is equal to 121 π¦ squared. Square rooting both sides of this equation gives us π is equal to 11π¦.

This means that the full factorisation of 100π₯ squared minus 121π¦ squared is 10π₯ plus 11π¦ multiplied by 10π₯ minus 11π¦. We could check this answer by expanding the two brackets, or parentheses, using the FOIL method.