A line drawn from vertex A of an equilateral triangle ABC meets BC at D and circumcircle at P
show that : PA = PB
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Step-by-step explanation:
Given A line drawn from vertex A of an equilateral triangle ABC meets BC at D and circumcircle at P show that : PA = PB + PC
- According to the question ABC is an equilateral triangle where BC meets at a point D and circumcircle at a point P. We need to find PA = PB + PC
- Now from the triangle AB = BC = CA
- Since angles are in same segment,
- So angle ABC = angle ACP = 60 degree
- Also angle ACB = angle ABP = 60 degree
- Now consider the triangle ACP,
- We have by cosine rule c^2 = a^2 + b^2 – 2ab cos c
- Or we can write it as cos c = a^2 + b^2 – c^2 / 2ab
- Or cos 60 = AP^2 + CP^2 – AC^2 / 2 (AP)(CP)
- 1/2 = Ap^2 + CP^2 – AC^2 / 2(AP)(CP)
- Or AP^2 – AC^2 = (AP)(CP) – CP^2 -----------1
- Now in triangle APB we have
- Cos 60 = AP^2 + BP^2 – AB^2 / 2 (AP)(BP)
- 1/2 = AP^2 + BP^2 – AB^2 / 2 (AP)(BP)
- Or AP^2 – AB^2 = (AP)(BP) – BP^2
- Or AP^2 – AC^2 = (AP)(BP) – BP^2 ------------2
- From equation 1 and 2 we get
- (AP)(PC) – PC^2 (AP)(PB) – PB^2
- Or PC^2 - PB^2 = (AP)(PC) – (AP)(PB)
- Or (PC + PB)(PC – PB) = AP(PC – PB) (since a^2 - b^2 = (a + b)(a – b)
- Or AP(PC – PB) = (PC + PB)(PC – PB)
- Or AP = (PC + PB)(PC – PB) / (PC – PB)
- Or AP = PC + PB
- So PA = PB + PC
Reference link will be
https://brainly.in/question/14874177
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