Question 37574
Hi,

When I was doing my GCSEs a long time ago, there was only one question on the paper I couldn't solve and it was almost the same as this one.

Firsst I'm going to assume that you're happy that we're really trying to solve

*[tex \frac{a}{4a+15}=1]

Fractions in algebra are really horrible, so we try and get rid of them if we can. Here we can multiply everything by *[tex 4a+15] to get rid of the fractions, so let's do that.

*[tex \frac{a}{4a+15}(4a+15)=4a+15]

*[tex a=4a+15]

*[tex 3a=-15]

*[tex a=-5]

The problem when multiplying by algebraic expressions is that we may accidently multiply by zero, which leads to a pointless equation. So here when we multipled by *[tex 4a+15] we need to check we didn't multiply by 0. Well if a=-5 then *[tex 4a+15=-20] so everything is ok.

You should also put the answer back in and check everything works, but I'll leave that to you.

Hope that helps,
Kev