Question 891638: c
Answer by dkppathak(439)   (Show Source):
You can put this solution on YOUR website! find the perimeter of an isosceles triangle whose base is 20 cm. and the vertex angle is 120 degree
we know perpendicular drawn from vertex to opposite side is angle bisector and also divide side in two equal part . let equal base angle is X
vertex angle +x+x =180 (angle sum property of triangle )
X=30 degree
half of base will be 20/2=10 cm
hypotenuses / adjacent side = Sec30 degree
H/10 =2/sqrt3
equal side (H)=20/sqrt3= 20 sqrt3/3 =11.54cm
perimeter of isoslace triangle = 20+11.54+11.54= 43.08 cm approx
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