The tangents at the points (at1 2,2at1) , (at2 2,2at2) on the parabola y2=4ax are at right angles if_____
  1. t1t2= -2
  2. t1t2= 1
  3. t1t2= 2
  4. t1t= -1

Equation of tangent at a point Pt is given byy=xt+atComparing with y=mx+c, slope of tangentm=1tFor point Aat12,2at1 slope of tangentm1=1t1For point Bat22,2at2 slope of tangentm2=1t2If two lines are perpendicular then product of their slope is -1m1m2=-11t1×1t2=-1t1t2=-1

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