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In $$\triangle MNL$$, line NP bisects the angle MNL. If NP : NL = 2 : 3 and angle MNL =Β $$120^\circ$$. Then NP : NL : MN is:
Let the value of MN be p
Since NP is the angular bisector
NP=Β $$\ \frac{\ 2\times\ MN\times\ NL}{MN+NL}\cos\theta\ \ $$
2x=$$\ \frac{\ 2\times\ p\times\ 3x}{p+3x}\cos60$$
p=6x
NP: NL: MN = 2:3:6
B is the correct answer.
Derivation for the length of angular bisector:
Let CP be the angular bisectorΒ ofΒ $$\angle\ ACB$$. And lengths of AB,BC,CA, CP,AP,PB be c,a,b,x,m,n respectively.
From triangles CPB and CPA using cosine rule we get:
$$n^2=a^2+x^2-2axCos\left(C\right)\ and\ m^2=b^2+x^2-2bxCos\left(C\right)$$
According to angle biscetor rule:Β $$\ \frac{b}{m}=\frac{a}{n}$$
.'.$$\frac{a^2}{b^2}=\frac{n^2}{m^2}$$=Β $$\frac{a^2+x^2β2axCos(C)}{\left(b^2+x^2β2bxCos(C\right)}$$.
$$\frac{a^2}{b^2}=\frac{a^2+x^2β2axCos(C)β}{b^2+x^2-2bxCos\left(C\right)}$$
Upon equating we get,Β $$(a^2βb^2)xβ2ab(aβb)Cos(C)=0$$
since x$$\ne\ 0$$,
x=$$\frac{2ab(aβb)Cos(C)}{a^2βb^2}$$
.'.x=$$\frac{2abCos(C)}{a+b}$$.
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