# Special equation solving

I would like to get x from the following function when the y is known and which + means If $1$ is bigger than x its equal $1 - x$ and else it's equal zero. Also, + means If x is bigger than 5 its equal $x-5$ and else it's equal zero:

$$0.1 x + (\frac{1}{2} - \frac{(1-x)_{+}^2}{2}) + (\frac{(x-5)^{2}_{+}}{2}) = -\log(1-y)$$

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Write the left side as $$f(x)=\begin {cases} \frac 12(\frac x5+2x-x^2)&x \lt 1\\ \frac x{10}+\frac 12&1 \le x \lt 5\\ \frac 12(x^2-9.8x+26)&x \ge 5 \end {cases}$$ Given the right side, you can solve each of these and see if $x$ is in the correct range.

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Can you check your answer. I think , the first equation is right, the second should be 0.1x+0.5 , and the third should be 0.5(x^2-1.8x+26). Am I right or wrong? –  rose Jun 18 at 0:20
@rose: you are correct on the second. For the third, the $\frac 12(x-5)^2$ contributes $-\frac {10}2x$ and the leading $0.1x$ contributes $\frac 12(0.2x)$ –  Ross Millikan Jun 18 at 2:08