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Geometry Level 4


The answer is 17.

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2 solutions

Join FE, and FC . Since BCDE, is a rectangle, so BCDE is a circle. In quadrilateral BCDF sum of opposite angles D F B + B C D = 180. i t i s c y c l i c . B C D E F i s a c i r c l e . C E B = D E B D E C = 32. A n g l e s o n c h o r d F C , C D F = C E F , C D E F D E = C E B + B E F 90 41 = 32 + B E F . B E F = 17. I n q u a d r i l a t e r a l A F G E , s a t F , a n d E a r e 9 0 o , i t i s c y c l i c . G A B = B E F = 17 \text{Join FE, and FC .} \\ \text{Since BCDE, is a rectangle, so BCDE is a circle. }\\ \text{ In quadrilateral BCDF sum of opposite angles}\\ \angle DFB+\angle BCD=180. ~~~ \therefore ~ it ~ is ~cyclic. \\ \implies ~~ \color{#3D99F6}{BCDEF ~is ~a ~ circle.}\\ \angle CEB=\angle DEB - \angle DEC = 32.\\ Angles ~ on ~ chord ~ FC,~~\angle CDF =\angle CEF,\\ \implies ~ ~ \angle CDE - \angle FDE= \angle CEB+\angle BEF \\ \implies ~ ~90 - 41= 32+\angle BEF.~~~~\therefore ~\angle BEF=17.\\ In ~~ ~\color{#3D99F6} { quadrilateral ~ AFGE} ,\\ \angle s ~ at ~ F, ~ and ~ E ~are ~ 90^o, \therefore ~ it ~ is ~cyclic.\\ \therefore ~ \angle GAB= \angle BEF= \Large ~~~~~\color{#D61F06} {17}

Priyanshu Mishra
Feb 20, 2016

Observe that B F E D BFED , A F G E AFGE , B C D E BCDE are all cyclic quadrilaterals.

In B F E D BFED , we have F D E = F B E = 41 0 \angle FDE = \angle FBE = { 41 }^{ 0 } .

Also, in B C D E BCDE , we have D C E = 32 0 = D B E \angle DCE = { 32 }^{ 0 } = \angle DBE .

Now observe that in A B D \triangle ABD D F DF and B E BE are altitudes intersecting at G G .

Hence, G G is the orthocenter of A B D \triangle ABD which implies A G D = 180 0 A B D = 180 0 ( 41 0 + 32 0 ) = 107 0 . \angle AGD = { 180 }^{ 0 } - \angle ABD = { 180 }^{ 0 } - ({ 41 }^{ 0 } + { 32 }^{ 0 }) = { 107 }^{ 0 }.

As F G D FGD is a straight line, we have A G D + A G F = 180 0 \angle AGD + \angle AGF = { 180 }^{ 0 } F G A = 73 0 \Rightarrow \angle FGA = { 73 }^{ 0 } .

Applying angle sum rule in triangle F A G FAG , we get G A F = 17 0 . \angle GAF = \boxed { { 17 }^{ 0 } } .

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