Question

Triangle ABC is an isosceles triangle, with AB=AC, altitude AM=11cm. Let a point D be on AM so that AD=10cm. If angleBDC=3× angleBAC. The perimeter of the triangle is?​

Answer 1

Answer:

ANSWER

The figure is as shown in the attached image.

sinB=AB10=BC12

⇒BC=1.2AB=1.2AC

sin2A=ABBD=AB2BC=AB0.6AB=0.6

⇒cos2A=0.8andtan2A=0.80.6=43

⇒ADBD=43⇒BD=10×43=7.5

BC=2×BD=15