Geomery from Gmat Prep
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ershovici wrote:OA is C can someone explain.
We all agree that 1 and 2 alone are not sufficient. So A, B and D are out.
Lets test for C. I strongly recommend you draw this as we speak.
First lets mark up some missing angles with variables based on information given to us in 1 and 2.
Angle SUT = Angle STU ( equal sides of triangle SUT) Lets call this angle "a"
Angle RQB = Angle RSQ ( equal sides of triangle RQS) Lets call these angles "b"
Since RST is a straight line, then
a + b + x = pie ....................... Equation 1
Now lets look at quadrilaterlal PQSU.
Sum of all interior angles should be 2 pie.
two of the angles are supplimentary to a and b.
( pie - a ) + (pie - b) + x + pie/2 = 2 pie which simplifies to :
a + b -x = pie/2 .................................. Equation 2
At this point you know the information provided to you was sufficient. Mark your answer and move on. But since we are not in a middle of an exam lets solve it to death.
Lets say a+b is called J the junk variable we dont care about.
Two equations are
J + x = pie ....... New Equation 1
J - x = pie/2 ....... New Equation 2
Solve these simultaneous equations for J you get x = pie/4
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P + R + T = 180
R + T = 90 .............................(1)
******************************************
Option A)
making a small isosceles triangle on top
R + Q + S1 = 180
R + 2Q = 180
Q or S1 = 90 - R/2 ...................(2)
**********************************************
Option B)
simliarly
S2 or U = 90 - T/2 ...................(3)
**********************************************
add (2) and (3)
S1 + S2 = 180 - (R+T)/2
180 - X = 180 - (90)/2
X = 45
Hence, C.
R + T = 90 .............................(1)
******************************************
Option A)
making a small isosceles triangle on top
R + Q + S1 = 180
R + 2Q = 180
Q or S1 = 90 - R/2 ...................(2)
**********************************************
Option B)
simliarly
S2 or U = 90 - T/2 ...................(3)
**********************************************
add (2) and (3)
S1 + S2 = 180 - (R+T)/2
180 - X = 180 - (90)/2
X = 45
Hence, C.