Math

QuestionBDundefined\overrightarrow{\mathrm{BD}} bisects ABC\angle ABC. If mABD=(3x+15)m \angle ABD=(3x+15)^{\circ} and mDBC=(5x12)m \angle DBC=(5x-12)^{\circ}, find mABCm \angle ABC.

Studdy Solution

STEP 1

Assumptions1. BDundefined\overrightarrow{\mathrm{BD}} bisects ABC\angle A B C . mABD=(3x+15)m \angle A B D=(3 x+15)^{\circ}
3. mDBC=(5x12)m \angle D B C=(5 x-12)^{\circ}

STEP 2

Since BDundefined\overrightarrow{\mathrm{BD}} bisects ABC\angle A B C, the measure of ABD\angle A B D is equal to the measure of DBC\angle D B C.
mABD=mDBCm \angle A B D = m \angle D B C

STEP 3

Substitute the given expressions for mABDm \angle A B D and mDBCm \angle D B C into the equation.
(3x+15)=(5x12)(3 x+15)^{\circ} = (5 x-12)^{\circ}

STEP 4

olve the equation for xx.
3xx=15(12)3x -x = -15 - (-12)

STEP 5

implify the equation.
2x=3-2x = -3

STEP 6

Divide both sides of the equation by -2 to solve for xx.
x=32=1.5x = \frac{-3}{-2} =1.5

STEP 7

Now that we have the value of xx, we can find the measure of ABD\angle A B D or DBC\angle D B C by substituting x=1.5x =1.5 into either of the given expressions. Let's use mABD=(3x+15)m \angle A B D = (3 x+15)^{\circ}.
mABD=3(1.5)+15m \angle A B D =3(1.5) +15

STEP 8

Calculate the measure of ABD\angle A B D.
mABD=4.5+15=19.5m \angle A B D =4.5 +15 =19.5^{\circ}

STEP 9

Since BDundefined\overrightarrow{\mathrm{BD}} bisects ABC\angle A B C, the measure of ABC\angle A B C is twice the measure of ABD\angle A B D.
mABC=2×mABDm \angle A B C =2 \times m \angle A B D

STEP 10

Substitute the measure of ABD\angle A B D into the equation.
mABC=2×19.5m \angle A B C =2 \times19.5^{\circ}

STEP 11

Calculate the measure of ABC\angle A B C.
mABC=×19.5=39m \angle A B C = \times19.5^{\circ} =39^{\circ}The measure of ABC\angle A B C is 3939^{\circ}.

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