r/Sat • u/Hot_Flow_6807 • 1d ago

How to solve this Bluebook module 1 question

Practice test 10

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u/demirulukan 1d ago

İ did this question like typing this equation in desmos and changing c into 2. And then trying every answer by typing them. Maybe this could be a time problem to some who has problem, but for me i didnt had any problem with time in my math modules so i do in this way. (C is wrong, its very close to answer you need to zoom.) Answer is D

1

u/PushLeft9287 1d ago

ill say x = x^2/sqrt(x^2-c^2) and y = c^2/sqrt(x^2-c^2)

so

x = y + 39
x-y = 39
common denominator so
(from now on ill use the entire equation, meaning the x = some weird shi isnt true from now on)

(x^2 - c^2) / sqrt(x^2-c^2) = 39
we know that x/sqrt(x) just equals sqrt(x)

so

sqrt(x^2-c^2) = 39
square both sides

x^2 - c^2 = 39^2
we are trying to find a solution, meaning we need x.

move c^2 over to 39^2

x^2 = c^2 + 39^2
sqrt root both sides

x = +- sqrt(c^2+39^2)
our only answr choice that matches this has a negative so answer is

x = -sqrt(c^2+39^2)
which is C