Question

Find the perimeter of an isosceles triangle whose base is 40 cm and whose base angle is 70o

Answer 1

since the triangle is isosceles, the other two sides will have equal length. Let call the length of each side $x$ .

Draw a perpendicular from vertex to base

(Bisector of base)

You will get a right triangle with a leg $20 cm$ and one angle $70 degrees$

Hence can use $cosine$ $ratio$ to obtain other side.

$cos(70°)=\frac{20}{x}$

$x=\frac{20}{cos(70°)}=58.48cm$

Add up the sides to get perimeter

Perimeter $= 58.48+58.48+40=156.96$