Multiplying radicals

$$(4\sqrt{3})(-5\sqrt{21})$$

Question

Multiplying radicals

$$(4\sqrt{3})(-5\sqrt{21})$$

anonymous · Answer

$$\huge \color{blue}{(a \sqrt{b})(-c \sqrt{d}) = -ac \sqrt{b \times d}}$$

ledah · Answer

What is that exactly?

anonymous · Answer

put the values and solve..

anonymous · Answer

a = 4, b = 3. c = 5 and d= 21

Plug in the values..

ledah · Answer

Oh.

ledah · Answer

I don't know how to plug this into the formula i guess if that's what your going to call it

anonymous · Answer

You know the values of a, b, c and d??

ledah · Answer

yes.

anonymous · Answer

and you are getting that formula which I have written above??

anonymous · Answer

Substitute the value of a, b, c and d into that formula..

anonymous · Answer

$$\huge \color{blue}{(4 \sqrt{3})(-5 \sqrt{21}) = -4 \times 5 \sqrt{3 \times 21}}$$

anonymous · Answer

What is the problem you are facing in doing this much..??

ledah · Answer

I was never taught this in regular school. so I have to redo it over this summer in virtual school and my virtual school teacher is out for vacation until the 8th and thus begins my problem. I just don't get how to solve for this. It doesn't come easy to me seeing as I mix up numbers all the time

anonymous · Answer

What you get if you multiply -4 with 5??

ledah · Answer

-20