Question

1.if 18,a,b,-3 are in A.P then a+b=?
2.sum of number and its reciprocal is 50/7 then the number is
3.Y=3 & Y=-3x intersects at
4.if 1/x+1/y then (x+y)/x.y=?

Answer 1

Twice the middle term is sum of terms on either side.
2 a = 18 + b
2 b = a - 3
adding these two equations,  a + b = 15
==================
x + 1/x = 50/7
7 x^2 - 50 x + 7 = 0
(7x - 1)(x - 7) = 0        Number  is  x = 7 or  1/7
==========================
Y = 3  and    Y = - 3 x  will intersect at
   Y = 3 = - 3 x  =>  x = -1  ie., (-1, 3)
=============================
(x+y)/(xy)  = 1/y + 1/x