英文四邊形數學題2(15分)

Every interior angle in a square is 90 degree, so
3x = 90
x = 30
The diagonal line BD bisects an interior angle, which gives angleADB = angleABD = 45 degree, so
sin(45 degree) = cos(45 degree) = y/2
√(2)/2 = y/2
y = √(2)

1.
3x = 90 degrees (prop. of square)
x = 90 degrees / 3
x = 30 degrees

2.
AD
= AB (prop. of square)
= y

so
y² + y² = 2² cm (Pyth. thm)
2y² = 4 cm
y² = 4 cm / 2
y = √2 or -√2(rejected)
y = √2 cm

2009-02-01 21:06:11 補充：
y = √2 but not √2 cm