Melody

Have a look at this site.  :)

xxxxxxxxxxxxxxxx

$$\begin{pmatrix}
7&16&5 \\
\end{pmatrix} %
\times
\begin{pmatrix}
1 \\
1\\
1
\end{pmatrix}
=(7*1+16*1+5*1)=(28)$$

Is that what you mean?

or

2/9km in 9minutes

is

2/81km in 1 minute

is

2/81*60km in 1 hour

$${\frac{{\mathtt{2}}}{{\mathtt{81}}}}{\mathtt{\,\times\,}}{\mathtt{60}} = {\frac{{\mathtt{40}}}{{\mathtt{27}}}} = {\mathtt{1.481\: \!481\: \!481\: \!481\: \!481\: \!5}}$$     km/hour

5/7*35

you can do this on the site calc on the home page. 

Which bit is repeating?

Maybe, it is you that works in the forensic department.  

Thanks Chris    

lo8 ???????

$$\\atan(\frac{1}{4})=A-B\qquad (1)\\\\
atan(\frac{1}{3})=A+B\qquad(2)\\\\
(1)+(2)\\\\
atan(\frac{1}{4})+atan(\frac{1}{3})=2A\\\\
tan[atan(\frac{1}{4})+atan(\frac{1}{3})]=tan[2A]\\\\$$

$$$Now I am going to use the identity$\\\\
\boxed{tan(\theta_1+\theta_2)=\frac{tan(\theta_1)+tan(\theta_2)}{1-tan(\theta_1)tan(\theta_2)}}\\\\\\
tan(2A)\\\\
=tan[atan(\frac{1}{4})+atan(\frac{1}{3})]\\\\
=\frac{\frac{1}{4}+\frac{1}{3}}{1-\frac{1}{4}\times\frac{1}{3}}\\\\
=\frac{\frac{7}{12}}{1-\frac{1}{12}}\\\\
=\frac{7}{12}\div \frac{11}{12}\\\\
=\frac{7}{12}\times \frac{12}{11}\\\\
=\frac{7}{11}\\\\
$This answer is exact$$$