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Re: F is the midpoint of AE, and D is the midpoint of CE. Wh [#permalink]
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Hello guys, any hint why choices C and D are false?
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Re: F is the midpoint of AE, and D is the midpoint of CE. Wh [#permalink]
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if you redraw the figure as follow, then C and D not necessarily are true.

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triangle.png [ 35.83 KiB | Viewed 9182 times ]
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Re: F is the midpoint of AE, and D is the midpoint of CE. Wh [#permalink]
thanks
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Re: F is the midpoint of AE, and D is the midpoint of CE. Wh [#permalink]
For answer choice E, how do you know triangles ACF and FCE are equal in area ?
Thanks in advance!
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Re: F is the midpoint of AE, and D is the midpoint of CE. Wh [#permalink]
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Because CE is comprised of bases CD and DE of triangles CD F and DEF, re­spectively, the two triangles have the same height. Because CDF and DEF have equal bases and the same height, they must have the same area. (For a similar rea­son, triangles ACF and FCE must have equal areas; more on that later.)

Read carefully.

Ask if you do need further explanations. Sir

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Re: F is the midpoint of AE, and D is the midpoint of CE. Wh [#permalink]
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Carcass wrote:
A is right

Because DE is \(\frac{1}{2}\) of CE and FE is \(\frac{1}{2}\) of AE (i.e., corre­sponding sides have proportional lengths), and angle DEF is shared between /the two triangles, you can see that triangles ACE and FDE must be similar. Similar triangles have the further property that corresponding angles are of equal measure. Thus, for example, angle DFE equals angle CAE, and so FD is parallel to AC.

B is right

Looking at the two smaller triangles in the right half of the figure, you can see that triangle CD F and triangle DEF have collinear and equal “bases” (CD and DE), and share their third vertex (F), which is some fixed distance away from
CE. Because CE is comprised of bases CD and DE of triangles CD F and DEF, re­spectively, the two triangles have the same height. Because CDF and DEF have equal bases and the same height, they must have the same area. (For a similar rea­son, triangles ACF and FCE must have equal areas; more on that later.)

Choice E is right

Because triangles ACF and FCE must have equal areas as indicated above, you can see that the area of triangle ACE must be twice that of triangle ACF. Note that FD is parallel to AC due to (true) choice (A), and BF is perpendicular toFD. Therefore, BF must be perpendicular to AC as well. Put differently, AC can be regarded as the base, and BF the height, of triangle ACF. The area of triangle ACF equals ^ times AC x BF. The area of triangle ACE, which is twice that of ACF, must therefore equal AC x BF.



Choice E is right

Because triangles ACF and FCE must have equal areas as indicated above, you can see that the area of triangle ACE must be twice that of triangle ACF. Note that FD is parallel to AC due to (true) choice (A), and BF is perpendicular toFD. Therefore, BF must be perpendicular to AC as well. Put differently, AC can be regarded as the base, and BF the height, of triangle ACF. The area of triangle ACF equals ^ times AC x BF. The area of triangle ACE, which is twice that of ACF, must therefore equal AC x BF.


Edited : (The last line will be---) The area of triangle ACF equals = \(\frac{1}{2}\) * AC x BF. The area of triangle ACE, which is twice that of ACF, must therefore equal AC x BF.

Extended: ACF = \(\frac{1}{2}\) * AC x BF
=> 2 *ACF = AC x BF
so, ACE = AC x BF (as we know triangle ACE is twice of triangle ACF)
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Re: F is the midpoint of AE, and D is the midpoint of CE. Wh [#permalink]
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