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With usual notation in Delta ABC, the nu...

With usual notation in `Delta ABC,` the numerical value of
`((a+b+c)/(r_(1)+r_(2)+r_(3))) ((a)/(r_(1))+(b)/(r _(2))+ (c)/(r_(3)))` is

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To solve the problem, we need to find the numerical value of the expression: \[ \frac{(a+b+c)}{(r_1 + r_2 + r_3)} \left( \frac{a}{r_1} + \frac{b}{r_2} + \frac{c}{r_3} \right) \] where \( r_1, r_2, r_3 \) are the exradii of triangle \( ABC \). ### Step 1: Define the exradii The exradii \( r_1, r_2, r_3 \) can be expressed in terms of the area \( \Delta \) of triangle \( ABC \) and the semi-perimeter \( S \): - \( r_1 = \frac{\Delta}{S - a} \) - \( r_2 = \frac{\Delta}{S - b} \) - \( r_3 = \frac{\Delta}{S - c} \) ### Step 2: Substitute the exradii into the expression Now we substitute \( r_1, r_2, r_3 \) into the expression: \[ r_1 + r_2 + r_3 = \frac{\Delta}{S - a} + \frac{\Delta}{S - b} + \frac{\Delta}{S - c} \] ### Step 3: Simplify the denominator To simplify \( r_1 + r_2 + r_3 \): \[ r_1 + r_2 + r_3 = \Delta \left( \frac{1}{S - a} + \frac{1}{S - b} + \frac{1}{S - c} \right) \] Finding a common denominator, we get: \[ r_1 + r_2 + r_3 = \Delta \cdot \frac{(S - b)(S - c) + (S - a)(S - c) + (S - a)(S - b)}{(S - a)(S - b)(S - c)} \] ### Step 4: Substitute into the main expression Now substituting back into the main expression: \[ \frac{(a+b+c)}{r_1 + r_2 + r_3} \left( \frac{a}{r_1} + \frac{b}{r_2} + \frac{c}{r_3} \right) \] ### Step 5: Simplify the first part The first part becomes: \[ \frac{(a+b+c)}{\Delta \cdot \frac{(S - b)(S - c) + (S - a)(S - c) + (S - a)(S - b)}{(S - a)(S - b)(S - c)}} \] ### Step 6: Simplify the second part The second part can be simplified as follows: \[ \frac{a}{r_1} + \frac{b}{r_2} + \frac{c}{r_3} = \frac{a(S - a)}{\Delta} + \frac{b(S - b)}{\Delta} + \frac{c(S - c)}{\Delta} \] This simplifies to: \[ \frac{1}{\Delta} \left( a(S - a) + b(S - b) + c(S - c) \right) \] ### Step 7: Combine both parts Combining both parts, we get: \[ \frac{(a+b+c)}{\Delta} \cdot \frac{(a(S - a) + b(S - b) + c(S - c))}{(S - b)(S - c) + (S - a)(S - c) + (S - a)(S - b)} \] ### Step 8: Evaluate the expression After simplifying and substituting \( S = \frac{a+b+c}{2} \), we can evaluate the expression. Ultimately, through simplification, we find that the numerical value of the entire expression is: \[ \boxed{4} \]
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