Question

What is the length of BC?

Answer 1

ABD is a right triangle with legs AB and AD and hypotenuse BD
therefore, you can use the formula

a^2 + b^2 = c^2 to find the hypotenuse c since you are given each leg

now, looking at triangle BCD, BD is the hypotenuse and BC and CD are the legs, so again, you can use a^2 + b^2 = c^2 to find the leg BC