SAT Subject Test Mathematics Level 1

Figure  3

To get the answer to this question, you need to know about equilateral, 45-45-
90, and 30-60-90 triangles. If you drop an altitude from B through D, you will
divide the equilateral triangle into two 30-60-90 triangles, and you will divide
the right isosceles (or 45-45-90) triangle into two smaller right isosceles
triangles:

In  Figure  3,  ∆ABC    is  equilateral and ∆ADC    is  isosceles.  If  AC  =   1,

what    is  the distance    from    B   to  D?

1.

(A) 0.286

(B) 0.318

(C) 0.333

(D) 0.366

(E) 0.383