Find the perimeter of a parcel of land in a shape of isosceles triangle

whose base is 40 cm and whose base angle is 70°. Provide an
Illustration.

in right triangles

sin = opposite / hypotenuse
cos = adjacent / hypotenuse
tan = opposite/adjacent = sin/cos
always look for right triangles. For example if an isosceles triangle draw the altitude from the middle of the base to the intersection of the two equal sides.