# Math Help - [SOLVED] substitution

1. ## [SOLVED] substitution

if y=as+b/x and if y= 13 when x = 1 and y = 20 when x=2, find the values of a and b and the value of s for which y is a minimum.

I have tried substitution but i can't seem to get hte right answer maybe i'm doing it wrong

2. Originally Posted by chibiusagi
if y=as+b/x and if y= 13 when x = 1 and y = 20 when x=2, find the values of a and b and the value of s for which y is a minimum.

I have tried substitution but i can't seem to get hte right answer maybe i'm doing it wrong
do you mean $y = \frac {as + b}x$ or $y = as + \frac bx$ ?

anyway, use the first two things given to set up simulataneous equations to solve for a and b

then take the derivative of the function (with a and b plugged in) and set it equal to zero and solve for s. you can check that this is a minimum using the second derivative