IIT JEE , AIEEE Forum - Mathematics , Algebra

preetirocks

1.A fair coin is tossed repeatedly, if tail appears on first toss, then the probability of getting head on the fifth toss is??
2. Equation of pair of lines passing through (2,1) and perpendicular to 6x*+17xy+12y*=0
3. If focus and vertex of parabola are (0,2) and (0,4) respectively, then its equation is??

eragon007

1)--as the coin is a fair one its probability of getting a head even after infinite turns will be 1/2, hence ans is 1/2

2)substitute x=x-2
                  y=y-1
in the eqn of straight lines

3)focus=0,2
vertex = 0,4    => a = 2
the general eqn for p'bola is

(y-y')=4a(x-x')
y'=2   x'=0
hence equation is
(y-2)=-8x(as the p'bola opens in the 2nd quadrant)