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In ΔABC prove that (b+c-a)tan A2=(c+a-b)tan B2=(a+b-c)tan C2. - Mathematics and Statistics

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प्रश्न

In ΔABC prove that `(b + c - a) tan  "A"/(2) = (c + a - b)tan  "B"/(2) = (a + b - c)tan  "C"/(2)`.

बेरीज

उत्तर

`(b + c - a) tan  "A"/(2)`
= `(a + b + c - 2a). sqrt(((s - b)(s - c))/(s(s - a)`

= `(2s - 2a).sqrt(((s - b)(s - c))/(s(s - a)`

= `2sqrt(((s - a)(s - b)(s - c))/s`  ....(1)

`(c + a - b) tan  "B"/(2)`
= `(a + b + c - 2b). sqrt(((s - a)(s - c))/(s(s - b)`

= `(2s - 2b).sqrt(((s - a)(s - c))/(s(s - b)`

= `2sqrt(((s - a)(s - b)(s - c))/s`                 ...(2)

`(a + b - c) tan  "C"/(2)`
= `(a + b + c - 2c). sqrt(((s - a)(s - b))/(s(s - c)`

= `(2s - 2c).sqrt(((s - a)(s - b))/(s(s - c)`

= `2sqrt(((s - a)(s - b)(s - c))/s`                 ...(3)

From (1), (2) an (3), we get

`(b + c - a)tan  "A"/(2) = (c + a - b)tan  "B"/(2) = (a + b - c)tan  "C"/(2)`.

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पाठ 3: Trigonometric Functions - Exercise 3.2 [पृष्ठ ८८]

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