Ratios/equations

**requal** · January 22nd 2009, 08:37 PM

If a:b=3:5, find the value of $\dfrac{a}{\sqrt{b^2-a^2}}$

**Jhevon** · January 22nd 2009, 09:35 PM

Originally Posted by requal

If a:b=3:5, find the value of $\dfrac{a}{\sqrt{b^2-a^2}}$

note that we have $\frac ab = \frac 35$ , that is, $a = \frac 35b$

replace $a$ with this expression in $\frac a{\sqrt{b^2 - a^2}}$ and simplify

**requal** · January 22nd 2009, 11:26 PM

i dont think that works as (3/5b)^2 is larger than b^2 thus creating a negative number under a square root?

**Jhevon** · January 23rd 2009, 12:13 AM

Originally Posted by requal

i dont think that works as (3/5b)^2 is larger than b^2 thus creating a negative number under a square root?

1 - 9/25 is positive. so you have 1b^2 - (9/25)b^2 = (16/25)b^2. how is this negative?

**requal** · January 23rd 2009, 02:36 AM

yep, sorry I had mental diaharea

thanks anyway

Thread: Ratios/equations