Trikona Asana - The Sanskrit word tri means three and kona means corner or angle. Thus "three corner or three angle posture" is often called the triangle posture. This posture is also known as the utthita trikona-asana. Utthita means stretched or extended thus this is the Extended Triangle Pose.
Instruction -
Stand with the feet together and the arms by your sides (see the tada-asana).
Separate the feet slightly further than shoulder distance apart.
Inhale and raise both arms straight out from the shoulders parallel to the floor with the palms facing down.
Exhale slowly while turning the torso to the left, bend at the waist and bring the right hand down to the left ankle. The palm of the right hand is placed along the outside of the left ankle. The left arm should be extended upward. Both legs and arms are kept straight without bending the knees and elbows.
Turn the head upward to the left and gaze up at the fingertips of the left hand. Inhale and return to a standing position with the arms outstretched.
Hold this position for the duration of the exhaled breath. Exhale and repeat steps 4 - 6 on the opposite side.
The Benefits are as follows

Stretches and strengthens the thighs, knees, and ankles
Stretches the hips, groins, hamstrings, and calves; shoulders, chest, and spine
Stimulates the abdominal organs
Helps relieve stress
Improves digestion
Helps relieve the symptoms of menopause
Relieves backache, especially through second trimester of pregnancy
Therapeutic for anxiety, flat feet, infertility, neck pain, osteoporosis, and sciatica