Question

Given that f(x)=2x -5, how do you find the value of x that makes f(x)=15?

Answer 1

`x=10`

Explanation:

`\color(red)(f(x)=2x-5)` and `\color(red)(f(x))=15`
therefore...
`2x-5=f(x)=15\rArr2x-5=15`
so you now have an equation to solve:
`2x-5=15`

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add 5 to both sides... `2x\cancel(-5+5)=15+5`
simplify `2x=20`
divide both sides by 20... `(\cancel(2)x)/\cancel(2)=20/2`
simplify `x=20/2=10`