Factorise 16−49h2 completely.

Sure, here is the step by step solution:

The given expression is 16 - 49h^2.

This is a difference of squares, which can be factored as follows:

A difference of squares is an expression of the form a^2 - b^2 and it can be factored as (a - b)(a + b).

Here, 16 is the square of 4 (since 4^2 = 16) and 49h^2 is the square of 7h (since (7h)^2 = 49h^2).

So, we can write 16 - 49h^2 as (4)^2 - (7h)^2.

Therefore, by applying the difference of squares, we get:

16 - 49h^2 = (4 - 7h)(4 + 7h).