**30 points*** assist will get brainiest i really need !
describe how you can use a double-angle formula or a half-angle formula to derive the formula for the area of an isosceles triangle. use a labeled sketch to illustrate your derivation. then write two examples that show how your formula can be used.

let the equal sides of the triangle be of length "a"  . let the angle between these two sides be " x  ". Then drop a perpendicular from the vertex to the base.  now u have 2 similar triangles  .the angle between the perpendicular and one of the equal sides is now (x/2)  . length of perpendicular = a cos(x/2)  length of base = 2a sin(x/2)  . area of triangle = (1/2) 2sin(x/2) cos(x/2) a-square  

= (1/2) (sin x) a-square

answer: 230 miles ( vote ! )

step-by-step explanation:

180.39 minus 17.99 equals 162.4

then divide 162.4 by .80 to get 230