We need to find the size of the reflex angle $BCD$ in the given figure. We have a triangle $ABD$ with angles $33^\circ$ at $D$, $51^\circ$ at $A$, and $25^\circ$ at $B$. We need to find the reflex angle at vertex $C$.

GeometryAnglesTrianglesReflex AngleAngle Calculation
2025/6/3

1. Problem Description

We need to find the size of the reflex angle BCDBCD in the given figure. We have a triangle ABDABD with angles 3333^\circ at DD, 5151^\circ at AA, and 2525^\circ at BB. We need to find the reflex angle at vertex CC.

2. Solution Steps

First, we calculate the angle ADBADB. The sum of the angles in the triangle ABDABD is 180180^\circ.
A+B+D=180A + B + D = 180^\circ
51+25+ADB=18051^\circ + 25^\circ + ADB = 180^\circ
76+ADB=18076^\circ + ADB = 180^\circ
ADB=18076=104ADB = 180^\circ - 76^\circ = 104^\circ
Then, we look for the angle BCDBCD. We are given angle BDC=33BDC = 33^\circ and angle DBC=25DBC = 25^\circ. We know that BCDBCD is exterior angle of triangle BCDBCD, so
BDA=BCD+DBC+BDC=58BDA = BCD + DBC + BDC=58
We are looking for angle BCDBCD. Let's look at the diagram differently.
Let angle BCA=xBCA=x and angle DCA=yDCA = y. The sum of the angles in triangle ABCABC is 180, so
x+51+25=180x+51+25=180, giving x=18076=104x=180-76 = 104.
The sum of the angles in triangle ADCADC is 180, so
y+51+33=180y+51+33=180, giving y=18084=96y=180-84 = 96.
Angle BCDBCD equals x+yx+y. Therefore, the normal angle at C=104+96=200C = 104 + 96 = 200. But the angle 200200 should be 360360^\circ - x. However, instead we can write BCD=180xBCD = 180^\circ - x, where xx is the interior angle at vertex CC.
The total angles around point CC is 360360^\circ. The normal angle at CC is 360360 - reflex angle at C.
To determine the angle ACBACB and ACDACD, we can find the missing angles.
We know BAC=51,ABC=25,ADC=33\angle BAC = 51^\circ, \angle ABC = 25^\circ, \angle ADC = 33^\circ.
ACB=1805125=104\angle ACB = 180 - 51 - 25 = 104^\circ
ACD=1805133=96\angle ACD = 180 - 51 - 33 = 96^\circ
The angle BCDBCD = 104+96=200104+96 =200^\circ.
ReflexBCD=360BCDReflex\,BCD = 360 - BCD.
ReflexBCD=360(25+33+51)=36068=202Reflex\,BCD = 360 - (25 + 33 +51)=360-68=202
ReflexBCD=360200=160Reflex\,BCD = 360-200 = 160^\circ
The angle at CC is 1802533=122180 - 25 - 33 = 122. So Reflex=360122=238Reflex=360-122=238
Therefore, BCD\angle BCD is 25+33=58+X25+33 = 58^\circ + X where X is the adjacent angle. The reflex angle should be 360BCD360^\circ - \angle BCD = 360104=302360 - 104 = 302
Let's name the intersection EE. In triangle ABEABE, AEB=180(51+25)=104\angle AEB = 180 - (51 + 25) = 104. Therefore DEC=104\angle DEC = 104 as they are vertically opposite angles.
Then, in triangle DECDEC, the angle at C, DCE=180(104+33)=180137=43\angle DCE = 180 - (104 + 33) = 180 - 137 = 43.
Therefore the reflex angle at C, is 36043=317360 - 43 = 317.

3. Final Answer

317

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