Question: show that triangle abc is isosceles?
Answer: Triangle ABC is an isosceles . Therefore square on altitude from AB to C = AD^2 = AC^2 - { (1/2) AB}^2 = 18 - 49/4 = 18- 12.25 = 5.75. Therefore the area of the triangle = (1/2) *BC*AD = (1/2)*7* sqrt5.