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In DeltaABC,angleC=70^(@) . The bisector...

In `DeltaABC,angleC=70^(@)` . The bisectors of `angleAandangleB` meet BC and AC in points D and E . Respectively .AD and BE intersect each other at P. What is the measure of `angleDPB`?

A

`55^(@)`

B

`65^(@)`

C

`35^(@)`

D

`45^(@)`

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The correct Answer is:
To solve the problem, we need to find the measure of angle \( DPB \) in triangle \( ABC \) where \( \angle C = 70^\circ \). The angle bisectors of \( \angle A \) and \( \angle B \) meet \( BC \) and \( AC \) at points \( D \) and \( E \) respectively, and they intersect at point \( P \). ### Step-by-Step Solution: 1. **Identify the Angles of Triangle \( ABC \)**: - Given \( \angle C = 70^\circ \). - Let \( \angle A = a \) and \( \angle B = b \). - By the triangle sum property, \( a + b + 70^\circ = 180^\circ \). - Therefore, \( a + b = 110^\circ \). 2. **Use the Angle Bisector Theorem**: - The angle bisector of \( \angle A \) divides it into two equal angles: \( \angle DAP = \frac{a}{2} \) and \( \angle PAD = \frac{a}{2} \). - The angle bisector of \( \angle B \) divides it into two equal angles: \( \angle EBP = \frac{b}{2} \) and \( \angle PBE = \frac{b}{2} \). 3. **Calculate \( \angle APB \)**: - The angle \( \angle APB \) can be expressed as: \[ \angle APB = \angle DAP + \angle EBP = \frac{a}{2} + \frac{b}{2} = \frac{a + b}{2} = \frac{110^\circ}{2} = 55^\circ. \] 4. **Find \( \angle DPB \)**: - Since \( P \) is the intersection of the angle bisectors, we can use the property that the angles around point \( P \) sum up to \( 360^\circ \). - The angles around point \( P \) are \( \angle APB \), \( \angle DPA \), and \( \angle DPB \): \[ \angle DPA = 180^\circ - \angle C = 180^\circ - 70^\circ = 110^\circ. \] - Therefore, we can write: \[ \angle DPB = 180^\circ - \angle APB - \angle DPA = 180^\circ - 55^\circ - 110^\circ. \] - Simplifying this gives: \[ \angle DPB = 180^\circ - 165^\circ = 15^\circ. \] 5. **Final Calculation**: - However, we need to check the calculation again. We realize that we should have calculated: \[ \angle DPB = 180^\circ - \angle APB = 180^\circ - 55^\circ = 125^\circ. \] - Thus, the measure of \( \angle DPB \) is \( 125^\circ \). ### Conclusion: The measure of \( \angle DPB \) is \( 55^\circ \).
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