Question

I need to check if I am heading to the right way.

Answer 1

`12\sqrt[]{2}`

Step-by-step explanation:

The sketch of the situation is given below

We need to find length B.

Now Pythagoras's theorem gives

`B^2+(4\sqrt[]{7})^2=20^2`

which simplifies to

`B^2+112=400`

subtracting 112 from both sides gives

`B^2=400-112`
`B^2=288`

Taking the square root of both sides gives

`B=\sqrt[]{288}`

`\boxed{B=12\sqrt[]{2}\text{.}}`

which is our answer!