Geometry Problem. Post your solution in the comment box below.

Level: Mathematics Education, High School, Honors Geometry, College.

This entry contributed by Sumith Peiris, Moratuwa, Sri Lanka.

Details: Click on the figure below..

## Friday, July 13, 2018

### Geometry Problem 1363: Square, Angle Bisector, Perpendicular, 45 Degrees, Angle, Sketch, iPad Apps

Labels:
45 degrees,
angle bisector,
geometry problem,
perpendicular,
square

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BG = BC (BF: bisector of angle CBE; FG perpendicular to BE)

ReplyDeleteSo BG=BC= AB; (square ABCD)

So A,G,C on same circle with center at B;

Connect AC,GC.

Angle CAG = ½ angle GBC =angle GBF=angle FBC.

Because BG=BC= AB;

So angle BAG =angle AGB;

Angle BAG =45+ angle GBF ;

Angle AGB =angle GBF + angle AHB;

So angle AHB=45.

let m(ABE)=x

ReplyDelete=> m(GBH)=45-x/2 -------(1)

Since m(FGB)=m(FCB)=90 and BF bisector of m(CBE)

=> BCFG is concyclic and BG=BC

Triangle ABG is isosceles and m(BAG)=90-x/2----------(2)

From (1) and (2), m(H)=180-(90-x/2)-(x+45-x/2)

=>m(H)=45

triangle BGF = triangle BCF

ReplyDelete=> BC=BG=BA => BAG isosceles

let alpha=angle(ABE)

Consider triangle ABH :

angle(H) = 180 - angle(A) - angle(B) = 180 - (alpha+(90-alpha)/2) - (180-alpha)/2) = 45°

Florin Popa, Comănești, România.

ReplyDelete∆BGF≡∆BCF,=>GF ≡CF,BG ≡BC(1)

Ducem cercul cu centrul in B și rază BC, care trece prin punctele A și G. BF taie cercul in punctul P iar prelungirea lui BF taie cercul in M. Ducem diametrul CBN.

Din (1) rezultă că arcele (CP) ̂=(GP) ̂. Se arată ușor că ∆BMN≡∆BGP de unde rezultă că (MN) ̂=(GP) ̂.

Atunci unghiul AHB = (Arc AM-arc GP)/2 = (arc AM – arc MN)/2 = arc AN /2 = 90/2=45.

Is CF=FG,BC=BG=AB => β-α=45.But <BHG=<BGA-<GBH=β-α=45.

ReplyDelete