The measure.

Geometry Level 2

In the above diagram AB = AD . D C B = 2 3 \angle DCB = 23 ^ \circ . The measurement of D B C \angle DBC is ?

Note - B A D \angle BAD = 4 4 44 ^ \circ


The answer is 45.

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3 solutions

Nikhil Raj
Jun 6, 2017

Since, AB = AD A B D = A D B . . . . . . . . . . . . . . . . ( 1 ) I n A B D , B A D + A B D + B D A = 180 44 + A B D + B D A = 180 A B D + B D A = 136 S o , A B D = A D B = 136 2 = 68 ( B y ( 1 ) ) In B D C , we have e x t A D B = D B C + D C B D B C = 45 {\text{Since, AB = AD}} \implies \angle ABD = \angle ADB \quad ................(1) \\ In \triangle ABD, \\ \angle BAD + \angle ABD + \angle BDA = 180 \\ 44 + \angle ABD + \angle BDA = 180 \\ \angle ABD + \angle BDA = 136 \\ So, \angle ABD = \angle ADB = \dfrac{136}{2} = 68 \quad (By (1)) \\ {\text{In }} \triangle BDC, {\text{we have}} \\ ext\angle ADB = \angle DBC + \angle DCB \\ \therefore \angle DBC = \color{#3D99F6}{\boxed{45}}

DBC=(180-A)/2-C -> DBC=45

Dan Wilhelm
Jul 7, 2015

Triangle A B D ABD is isoceles, so A B D = A D B = ( 18 0 4 4 ) / 2 = 6 8 \angle ABD = \angle ADB = (180 ^\circ - 44 ^\circ)/2 = 68 ^\circ .

Knowing that two angles on the straight line A C AC sum to 18 0 180 ^\circ :

B D C = 18 0 A D B = 18 0 6 8 = 11 2 \angle BDC = 180 ^\circ - \angle ADB = 180 ^\circ - 68 ^\circ = 112 ^\circ .

Now we solve for the solution, D B C \angle DBC , knowing the angles in the triangle B D C BDC sum to 18 0 180 ^\circ :

D B C = 18 0 B D C D C B = 18 0 11 2 2 3 = 4 5 \angle DBC = 180 ^\circ - \angle BDC - \angle DCB = 180 ^\circ - 112 ^\circ - 23 ^\circ = 45 ^\circ .

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