In triangle ABC a straight line parallel to BC intersects AB and AC at D and E respectively. If AB = 2AD then DE : BC is
1). 2:3
2). 2:1
3). 1:2
4). 1:3
2. If x + y + z = 15 and x2 + y2 + z2 = 77, then find xy + yz + zx.
4. If x + 1/x = √13, then 3x/($x^{2}$-1) equal to
7. If x = (√5 + 1)/(√5 - 1) and y = (√5 - 1)/(√5 + 1), then find the value of x2 - y2.
10. What approximate value will come in place of the question mark (?) in following equations ?