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In `Delta ABC` with usual notation `r_1/(bc)+r_2/(ca)+r_3/(ab)` isA. `(1)/(2R) -(1)/(r )`B. `2R-r`C. `r-2R`D. `(1)/(r )-(1)/(2R)` |
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Answer» Correct Answer - 4 `(r_(1))/(bc)=(4R sin (A//2)cos(B//2)cos(c//2))/(2R sin B.2R sin c)` `=(sin(A//2))/(4R(sin(B//2)sin(C//2)` `=(sin^(2)(A//2))/(R )` `"So that" (r_(1))/(bc)+(r_(2))/(ca)+(r_(3))/(ab)` `=(1)/(r )[(sin^(2)(A//2)+sin^(2)(B//2)+sin^(2)(C//2)]` `=(1)/(2r)[3-(1+4 sin(A//2)sin(B//2)sin(C//2))]` `=(1)/(2r)[2-(r)/(R)]=1/r-1/R` |
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