Posso avere una spiegazione

((1 + 3/4 - 1/3)^2 - (3/12 - 1/3)^2)/(1 + 3/12) - 1/2 - 1/3=

=((17/12)^2 - (- 1/12)^2)/(1 + 3/12) - 1/2 - 1/3=

=((17/12)^2 - (- 1/12)^2)/(5/4) - 1/2 - 1/3=

=(17/12 + 1/12)·(17/12 - 1/12)/(5/4) - 1/2 - 1/3=

=3/2·(4/3)/(5/4) - 1/2 - 1/3=

=2/(5/4) - 1/2 - 1/3=

=8/5 - 1/2 - 1/3= 23/30

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$\small \left[\left(1+\dfrac{3}{4}-\dfrac{1}{3}\right)^2-\left(\dfrac{3}{12}-\dfrac{1}{3}\right)^2\right]÷\left(1+\dfrac{3}{17}\right)-\dfrac{1}{2}-\dfrac{1}{3} =$

$\small = \left[\left(\dfrac{12+9-4}{12}\right)^2-\left(\dfrac{3-4}{12}\right)^2\right]÷\left(\dfrac{17+3}{17}\right)-\dfrac{1}{2}-\dfrac{1}{3} =$

$\small = \left[\left(\dfrac{17}{12}\right)^2-\left(-\dfrac{1}{12}\right)^2\right]÷\dfrac{20}{17}-\dfrac{1}{2}-\dfrac{1}{3} =$

$\small = \left[\dfrac{289}{144}-\dfrac{1}{144}\right]·\dfrac{17}{20}-\dfrac{1}{2}-\dfrac{1}{3} =$

$\small = \dfrac{\cancel{288}^2}{\cancel{144}_1}·\dfrac{17}{20}-\dfrac{1}{2}-\dfrac{1}{3} =$

$\small = \cancel2^1·\dfrac{17}{\cancel{20}_{10}}-\dfrac{1}{2}-\dfrac{1}{3} =$

$\small = \dfrac{17}{10}-\dfrac{1}{2}-\dfrac{1}{3} =$

$\small = \dfrac{51-15-10}{30} =$

$\small = \dfrac{\cancel{26}^{13}}{\cancel{30}_{15}} =$

$\small = \dfrac{13}{15} $

A me risulta così, interpretando 3/17 nella terza parentesi, se provo con 3/12 mi viene come a  @lucianop quindi, salvo errori nel testo, ricontrolla ciò che hai scritto. Saluti.

((1 + 3/4 - 1/3)^2 - (3/12 - 1/3)^2) / (1 + 3/17) - 1/2 - 1/3

((17/12)^2 - (- 1/12)^2) / (1 + 3/17) - 1/2 - 1/3

((17/12)^2 - (- 1/12)^2) / (20/17) - 1/2 - 1/3

(17/12 + 1/12) * (17/12 - 1/12) / (20/17) - 1/2 - 1/3

3/2 * (4/3) / (20/17) - 1/2 - 1/3

2 / (20/17) - 1/2 - 1/3

34/20 - 1/2 - 1/3

(34 * 3 - 30 -20) / 60

52 / 60

13 / 15