1.

Let the harmonic mean of two positive real numbers a and b be 4, If q is a positive real number such that a, 5, q, b is an arithmetic progression, then the value(s) of |q -a| is (are)

Answer» `4=(2ab)/(a+b)`
`(ab)/(a+b)=2-(1)`
a,5,q,b->AP common diff. d
`a=5-d-(2)`
`q=a+2d`
`b=a+3d`
`b=5+2d-(3)`
`((5-d)(5+2d))/(10+d)=2`
`2d^2-3d-5=0`
`(2d-5)(d+1)=0`
`d=-1,5/2`
`d=-1`
`2|d|=2`.


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