please explain gmat prep question

yvonne12 wrote:ok, I want to know if I worked out this problem correctly.

sqrt 8^2 - 4^2


64-16=48

48= 6x8

2sqrt3 x 2sqrt2 and then all these numbers are added? to get to 7?

please explain how I can work out problems lsuch as this one.

Your question is not quiet clear ...
If you wanted the approximate value of
sqrt 8^2 - 4^2

you got it right in first step saying
=sqrt (64-16)= sqrt (48.)

Now considering sqrt (49.) =7 , Cant you say sqrt (48.) is close to 7


Now If you wanted to simplify that

sqrt 8^2 - 4^2

Remember a^2-b^2 = (a+b)(a-b) , applying this

sqrt (8^2 - 4^2) = sqrt ((8+4)(8-4)) = sqrt ( 12*4) = 4* sqrt(3)

now that is 4* 1.73 =6.92 ( wow, it is not a coincidence that it is close to 7)