dave13 wrote:
hello there
GMATPrepNow 
can you please explain how you combine both statements to get answer
Statement 1 tells us that x + y = 15
Statement 2 tells us that √(xy) = 6
and then you say
Recognize that (√x + √y)² = x + 2√(xy) + y I dont recognize this pattern in either of the statements
how can I recognize it looking at both statements where did you get this formula ?
I thought I should do square both sides of √(xy) = 6 so I am getting xy = 36 and also have x + y = 15 so I do something like this
x + y = 15 ---> x = 15-y and plug in here xy = 36
thank you in advance for taking time to explain and have a great gmat weekend
It's not easy to see that
(√x + √y)² = x + 2√(xy) + y, however when we see that we have information about x and y and we need to find the value of √x and √y and y, we might start looking for possible relationships that might help us. One relationship is that (√x)² = x and that (√y)² =y
From there, it's a matter of exploring what (√x + √y)² might look like.
We can use the FOIL method to expand (√x + √y)²
We get: (√x + √y)² = (√x + √y)(√x + √y) = x + √xy + √xy +y = x + 2√xy + y
At this point, we can see that our exploration has paid off.
Keep in mind that solving math questions involves little explorations like this. Sometimes those explorations take us closer to the solution; sometimes they take us nowhere, in which case we need to try something else.
Cheers,
Brent
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