Question

I need help in multiplying two square roots. (5*sqrt7-10*sqrt2)(4*sqrt7+8*sqrt2)=

Answer 1

You will be multiplying four pairs of square roots, not two.

Remember that (a + b)*(c + d)
= ac + ad + bc + bd

Now do the multiplying.
You will end up with two terms, 40 sqrt14 and -40 sqrt14 that cancel. The other two terms will not cancel, but you can get rid of the square roots