Question

5sqrt8 times 4sqrt7

Options:
16sqrt10
20sqrt15
40sqrt14
40


I know that you're supposed to keep what's inside in, and what's outside out. Using that rule got me to 20sqrt56. Not really sure what to do from here. I tried to simplify sqrt56, but it only got me 80sqrt14, which is obviously not one of the options. Any help would be appreciated. :)

Answer 1

ok you have a small mistake when you calculated 80sqrt(40)

Answer 2

80sqrt(14) i meant

Answer 3

you multiplied the outside by 4 instead of 2 as you divided the inside by 4

Answer 4

5(√8) * 4(√7)

20 * (√7) * √(4 * 2)

20 * (√7) * 2√2

40 * (√7) * √2 = 40√14

Answer 5

I went from 20sqrt56
to simplifying sqrt56

sqrt56
sqrt8 times 7
sqrt4 times 2 times 7
sqrt2 times 2 times 2 times 7

20 times 4sqrt2 times 7
80sqrt14

Answer 6

56 is 8*7
56 is 2*2*2*7
you can only take out things that come in pairs, because this is a square root.
when you take out a pair of things from the inside, it becomes one of those things on the outside
does that make any sense?

Answer 7

Yeah, since there's 2*2*2*7, you would bring out one pair of by multiplying 2 and 20?

Answer 8

yes

Answer 9

Oh I've figured it out. I made the mistake of multiplying the 2*2, getting 4, and then multiplying the 4 by 20. I've gotten a final answer of 40sqrt14.

Answer 10

and then you would have just 2*7 inside the sqrt

Answer 11

yes, you got it.
good job

Answer 12

20sqrd15

Answer 13

Thanks for your help :)