Plz solve
an isosceles triangle has a verticle angle of 108 degree and a base 20cm long calculate its altitude

The area of the triangle = 1/2 * base * altitude  = 1.2 * 20 * a = 10a

Work out the altitude (a):-

the altitude  forms a right angled triangle with vertex angle = 1/2*108 = 54

so tan 54 = 10 / a

a = 10 / tan 54  =  7.265

area of the triangle = 10 * 7.265 = 72.65 cm^2